Adding different sized/shaped displaced NumPy matrices





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9















In short: I have two matrices (or arrays):



import numpy

block_1 = numpy.matrix([[ 0, 0, 0, 0, 0],
[ 0, 0, 0, 0, 0],
[ 0, 0, 0, 0, 0],
[ 0, 0, 0, 0, 0]])

block_2 = numpy.matrix([[ 1, 1, 1],
[ 1, 1, 1],
[ 1, 1, 1],
[ 1, 1, 1]])


I have the displacement of block_2 in the block_1 element coordinate system.



pos = (1,1)


I want to be able to add them (quickly), to get:



[[0 0 0 0 0]
[0 1 1 1 0]
[0 1 1 1 0]
[0 1 1 1 0]]


In long: I would like a fast way to add two different shape matrices together, where one of the matrices can be displaced. The resulting matrix must have the shape of the first matrix, and the overlapping elements between the two matrices are summed. If there is no overlap, just the first matrix is returned unmutated.



I have a function that works fine, but it's kind of ugly, and elementwise:



def add_blocks(block_1, block_2, pos):
for i in xrange(0, block_2.shape[0]):
for j in xrange(0, block_2.shape[1]):
if (i + pos[1] >= 0) and (i + pos[1] < block_1.shape[0])
and (j + pos[0] >= 0) and (j + pos[0] < block_1.shape[1]):
block_1[pos[1] + i, pos[0] + j] += block_2[i,j]
return block_1


Can broadcasting or slicing perhaps do this?



I feel like maybe I'm missing something obvious.










share|improve this question































    9















    In short: I have two matrices (or arrays):



    import numpy

    block_1 = numpy.matrix([[ 0, 0, 0, 0, 0],
    [ 0, 0, 0, 0, 0],
    [ 0, 0, 0, 0, 0],
    [ 0, 0, 0, 0, 0]])

    block_2 = numpy.matrix([[ 1, 1, 1],
    [ 1, 1, 1],
    [ 1, 1, 1],
    [ 1, 1, 1]])


    I have the displacement of block_2 in the block_1 element coordinate system.



    pos = (1,1)


    I want to be able to add them (quickly), to get:



    [[0 0 0 0 0]
    [0 1 1 1 0]
    [0 1 1 1 0]
    [0 1 1 1 0]]


    In long: I would like a fast way to add two different shape matrices together, where one of the matrices can be displaced. The resulting matrix must have the shape of the first matrix, and the overlapping elements between the two matrices are summed. If there is no overlap, just the first matrix is returned unmutated.



    I have a function that works fine, but it's kind of ugly, and elementwise:



    def add_blocks(block_1, block_2, pos):
    for i in xrange(0, block_2.shape[0]):
    for j in xrange(0, block_2.shape[1]):
    if (i + pos[1] >= 0) and (i + pos[1] < block_1.shape[0])
    and (j + pos[0] >= 0) and (j + pos[0] < block_1.shape[1]):
    block_1[pos[1] + i, pos[0] + j] += block_2[i,j]
    return block_1


    Can broadcasting or slicing perhaps do this?



    I feel like maybe I'm missing something obvious.










    share|improve this question



























      9












      9








      9


      2






      In short: I have two matrices (or arrays):



      import numpy

      block_1 = numpy.matrix([[ 0, 0, 0, 0, 0],
      [ 0, 0, 0, 0, 0],
      [ 0, 0, 0, 0, 0],
      [ 0, 0, 0, 0, 0]])

      block_2 = numpy.matrix([[ 1, 1, 1],
      [ 1, 1, 1],
      [ 1, 1, 1],
      [ 1, 1, 1]])


      I have the displacement of block_2 in the block_1 element coordinate system.



      pos = (1,1)


      I want to be able to add them (quickly), to get:



      [[0 0 0 0 0]
      [0 1 1 1 0]
      [0 1 1 1 0]
      [0 1 1 1 0]]


      In long: I would like a fast way to add two different shape matrices together, where one of the matrices can be displaced. The resulting matrix must have the shape of the first matrix, and the overlapping elements between the two matrices are summed. If there is no overlap, just the first matrix is returned unmutated.



      I have a function that works fine, but it's kind of ugly, and elementwise:



      def add_blocks(block_1, block_2, pos):
      for i in xrange(0, block_2.shape[0]):
      for j in xrange(0, block_2.shape[1]):
      if (i + pos[1] >= 0) and (i + pos[1] < block_1.shape[0])
      and (j + pos[0] >= 0) and (j + pos[0] < block_1.shape[1]):
      block_1[pos[1] + i, pos[0] + j] += block_2[i,j]
      return block_1


      Can broadcasting or slicing perhaps do this?



      I feel like maybe I'm missing something obvious.










      share|improve this question
















      In short: I have two matrices (or arrays):



      import numpy

      block_1 = numpy.matrix([[ 0, 0, 0, 0, 0],
      [ 0, 0, 0, 0, 0],
      [ 0, 0, 0, 0, 0],
      [ 0, 0, 0, 0, 0]])

      block_2 = numpy.matrix([[ 1, 1, 1],
      [ 1, 1, 1],
      [ 1, 1, 1],
      [ 1, 1, 1]])


      I have the displacement of block_2 in the block_1 element coordinate system.



      pos = (1,1)


      I want to be able to add them (quickly), to get:



      [[0 0 0 0 0]
      [0 1 1 1 0]
      [0 1 1 1 0]
      [0 1 1 1 0]]


      In long: I would like a fast way to add two different shape matrices together, where one of the matrices can be displaced. The resulting matrix must have the shape of the first matrix, and the overlapping elements between the two matrices are summed. If there is no overlap, just the first matrix is returned unmutated.



      I have a function that works fine, but it's kind of ugly, and elementwise:



      def add_blocks(block_1, block_2, pos):
      for i in xrange(0, block_2.shape[0]):
      for j in xrange(0, block_2.shape[1]):
      if (i + pos[1] >= 0) and (i + pos[1] < block_1.shape[0])
      and (j + pos[0] >= 0) and (j + pos[0] < block_1.shape[1]):
      block_1[pos[1] + i, pos[0] + j] += block_2[i,j]
      return block_1


      Can broadcasting or slicing perhaps do this?



      I feel like maybe I'm missing something obvious.







      python numpy






      share|improve this question















      share|improve this question













      share|improve this question




      share|improve this question








      edited Mar 27 '12 at 22:58









      Peter Mortensen

      13.9k1987114




      13.9k1987114










      asked Mar 27 '12 at 9:00









      fraxelfraxel

      26.2k67586




      26.2k67586
























          5 Answers
          5






          active

          oldest

          votes


















          4














          You just have to find the overlapping range, and then add the arrays using slicing.



          b1 = np.zeros((4,5))
          b2 = np.ones((4,3))
          pos_v, pos_h = 2, 3 # offset
          v_range1 = slice(max(0, pos_v), max(min(pos_v + b2.shape[0], b1.shape[0]), 0))
          h_range1 = slice(max(0, pos_h), max(min(pos_h + b2.shape[1], b1.shape[1]), 0))

          v_range2 = slice(max(0, -pos_v), min(-pos_v + b1.shape[0], b2.shape[0]))
          h_range2 = slice(max(0, -pos_h), min(-pos_h + b1.shape[1], b2.shape[1]))

          b1[v_range1, h_range1] += b2[v_range2, h_range2]


          They're added in-place, but you could also create a new array. I might have missed some corner cases, though, but it seems to work fine.






          share|improve this answer


























          • I ended up doing something very similar to this. The ability to create slice objects is really great, thanks for that!

            – fraxel
            Mar 27 '12 at 12:06











          • I think the v_range1 and h_range1 code is missing a final closing ')'.

            – David Poole
            Mar 28 '12 at 15:03











          • Thanks! I just fixed that.

            – jorgeca
            Mar 28 '12 at 17:58



















          14














          An easy solution that looks like MATLAB solution is:



          import numpy as np

          block1 = np.zeros((5,4))
          block2 = np.ones((3,2))

          block1[1:4,2:4] += block2 # use array slicing

          print(block1)

          [[0. 0. 0. 0.]
          [0. 0. 1. 1.]
          [0. 0. 1. 1.]
          [0. 0. 1. 1.]
          [0. 0. 0. 0.]]




          So package it as a reusable function:



          import numpy as np

          def addAtPos(mat1, mat2, xypos):
          """
          Add two matrices of different sizes in place, offset by xy coordinates
          Usage:
          - mat1: base matrix
          - mat2: add this matrix to mat1
          - xypos: tuple (x,y) containing coordinates
          """
          x, y = xypos
          ysize, xsize = mat2.shape
          xmax, ymax = (x + xsize), (y + ysize)
          mat1[y:ymax, x:xmax] += mat2
          return mat1

          block1 = np.zeros((5,4))
          block2 = np.ones((3,2))
          pos = (2,1)
          print(addAtPos(block1, block2, pos))

          [[0. 0. 0. 0.]
          [0. 0. 1. 1.]
          [0. 0. 1. 1.]
          [0. 0. 1. 1.]
          [0. 0. 0. 0.]]





          share|improve this answer





















          • 1





            This is looking good,and much more readable. But if some of block_2 falls outside block_1 it fails. Easy to fix of course.

            – fraxel
            Mar 27 '12 at 9:45











          • @fraxel Yeah, you can always add size checking if needed ;)

            – EwyynTomato
            Mar 27 '12 at 9:52



















          2














          This is great, and here's how to extend the addition to a 3D matrix by adding a few lines to jorgeca's code:



          import numpy as np

          #two 3d arrays, of different size.
          b1 = np.zeros((5,5,5), dtype=np.int) # a 5x5x5 matrix of zeroes
          b2 = np.ones((3,3,3), dtype=np.int) # a 3x3x3 matrix of ones

          pos_v, pos_h, pos_z = 2, 2, 2 # a 3d offset -> to plonk b2 in the corner of b1

          v_range1 = slice(max(0, pos_v), max(min(pos_v + b2.shape[0], b1.shape[0]), 0))
          h_range1 = slice(max(0, pos_h), max(min(pos_h + b2.shape[1], b1.shape[1]), 0))
          z_range1 = slice(max(0, pos_z), max(min(pos_z + b2.shape[2], b1.shape[2]), 0))

          v_range2 = slice(max(0, -pos_v), min(-pos_v + b1.shape[0], b2.shape[0]))
          h_range2 = slice(max(0, -pos_h), min(-pos_h + b1.shape[1], b2.shape[1]))
          z_range2 = slice(max(0, -pos_z), min(-pos_z + b1.shape[2], b2.shape[2]))

          b1[v_range1, h_range1, z_range1] += b2[v_range2, h_range2, z_range2]


          This might help someone who wants to do the same in 3d (like me).






          share|improve this answer































            1














            I'm sure there is a fast NumPy way to do this, but there is a more efficient way to do it even in normal Python:



            block_1 = [ [ 0, 0, 0, 0, 0],
            [ 0, 0, 0, 0, 0],
            [ 0, 0, 0, 0, 0],
            [ 0, 0, 0, 0, 0]]

            block_2 = [ [ 1, 1, 1],
            [ 1, 1, 1],
            [ 1, 1, 1],
            [ 1, 1, 1]]

            pos = (1, 1)

            x, y = pos

            # width of the rows in block_2
            length = len(block_2[0])

            # skip the first y rows
            for row_1, row_2 in zip(block_1[y:], block_2):
            # set length elements offset by x to the sum.
            row_1[x:length + x] = map(sum, zip(row_2, row_1[x:length + x]))

            print 'n'.join(' '.join(map(str, row)) for row in block_1)

            """
            0 0 0 0 0
            0 1 1 1 0
            0 1 1 1 0
            0 1 1 1 0
            """





            share|improve this answer































              1














              Here's @jorgeca's great code as a function, with some tests - I expanded the slices to try to make it a little more readable:



              import numpy as np


              def addAtPos(matrix1, matrix2, xypos, inPlace=False):
              """
              Add matrix2 into matrix1 at position xypos (x,y), in-place or in new matrix.
              Handles matrix2 going off edges of matrix1.
              """

              x, y = xypos
              h1, w1 = matrix1.shape
              h2, w2 = matrix2.shape

              # get slice ranges for matrix1
              x1min = max(0, x)
              y1min = max(0, y)
              x1max = max(min(x + w2, w1), 0)
              y1max = max(min(y + h2, h1), 0)

              # get slice ranges for matrix2
              x2min = max(0, -x)
              y2min = max(0, -y)
              x2max = min(-x + w1, w2)
              y2max = min(-y + h1, h2)

              if inPlace:
              # add matrix2 into matrix1, in place
              matrix1[y1min:y1max, x1min:x1max] += matrix2[y2min:y2max, x2min:x2max]
              else:
              # create and return a new matrix
              matrix1copy = matrix1.copy()
              matrix1copy[y1min:y1max, x1min:x1max] += matrix2[y2min:y2max, x2min:x2max]
              return matrix1copy


              def test_addAtPos():

              matrix1 = np.zeros((2,2))
              matrix2 = np.ones((2,2))

              test(addAtPos(matrix1, matrix2, ( 0, 0)), [[1,1],[1,1]])
              test(addAtPos(matrix1, matrix2, ( 2, 2)), [[0,0],[0,0]])
              test(addAtPos(matrix1, matrix2, (-1,-1)), [[1,0],[0,0]])
              test(addAtPos(matrix1, matrix2, ( 1,-1)), [[0,1],[0,0]])
              test(addAtPos(matrix1, matrix2, ( 1, 1)), [[0,0],[0,1]])
              test(addAtPos(matrix1, matrix2, (-1, 1)), [[0,0],[1,0]])


              def test(actual, expected, message=''):
              "Compare actual and expected values and print OK or FAIL"
              passed = (actual == expected)
              if type(passed) == np.ndarray:
              passed = passed.all()
              actual = str(actual).replace('n', '')
              expected = str(expected).replace('n', '')
              if passed:
              print('[OK] ', message, actual)
              else:
              print('[FAIL]', message, actual, ' != expected value of', expected)


              test_addAtPos()


              Output:



              [OK]    [[1. 1.] [1. 1.]]
              [OK] [[0. 0.] [0. 0.]]
              [OK] [[1. 0.] [0. 0.]]
              [OK] [[0. 1.] [0. 0.]]
              [OK] [[0. 0.] [0. 1.]]
              [OK] [[0. 0.] [1. 0.]]





              share|improve this answer
























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                5 Answers
                5






                active

                oldest

                votes








                5 Answers
                5






                active

                oldest

                votes









                active

                oldest

                votes






                active

                oldest

                votes









                4














                You just have to find the overlapping range, and then add the arrays using slicing.



                b1 = np.zeros((4,5))
                b2 = np.ones((4,3))
                pos_v, pos_h = 2, 3 # offset
                v_range1 = slice(max(0, pos_v), max(min(pos_v + b2.shape[0], b1.shape[0]), 0))
                h_range1 = slice(max(0, pos_h), max(min(pos_h + b2.shape[1], b1.shape[1]), 0))

                v_range2 = slice(max(0, -pos_v), min(-pos_v + b1.shape[0], b2.shape[0]))
                h_range2 = slice(max(0, -pos_h), min(-pos_h + b1.shape[1], b2.shape[1]))

                b1[v_range1, h_range1] += b2[v_range2, h_range2]


                They're added in-place, but you could also create a new array. I might have missed some corner cases, though, but it seems to work fine.






                share|improve this answer


























                • I ended up doing something very similar to this. The ability to create slice objects is really great, thanks for that!

                  – fraxel
                  Mar 27 '12 at 12:06











                • I think the v_range1 and h_range1 code is missing a final closing ')'.

                  – David Poole
                  Mar 28 '12 at 15:03











                • Thanks! I just fixed that.

                  – jorgeca
                  Mar 28 '12 at 17:58
















                4














                You just have to find the overlapping range, and then add the arrays using slicing.



                b1 = np.zeros((4,5))
                b2 = np.ones((4,3))
                pos_v, pos_h = 2, 3 # offset
                v_range1 = slice(max(0, pos_v), max(min(pos_v + b2.shape[0], b1.shape[0]), 0))
                h_range1 = slice(max(0, pos_h), max(min(pos_h + b2.shape[1], b1.shape[1]), 0))

                v_range2 = slice(max(0, -pos_v), min(-pos_v + b1.shape[0], b2.shape[0]))
                h_range2 = slice(max(0, -pos_h), min(-pos_h + b1.shape[1], b2.shape[1]))

                b1[v_range1, h_range1] += b2[v_range2, h_range2]


                They're added in-place, but you could also create a new array. I might have missed some corner cases, though, but it seems to work fine.






                share|improve this answer


























                • I ended up doing something very similar to this. The ability to create slice objects is really great, thanks for that!

                  – fraxel
                  Mar 27 '12 at 12:06











                • I think the v_range1 and h_range1 code is missing a final closing ')'.

                  – David Poole
                  Mar 28 '12 at 15:03











                • Thanks! I just fixed that.

                  – jorgeca
                  Mar 28 '12 at 17:58














                4












                4








                4







                You just have to find the overlapping range, and then add the arrays using slicing.



                b1 = np.zeros((4,5))
                b2 = np.ones((4,3))
                pos_v, pos_h = 2, 3 # offset
                v_range1 = slice(max(0, pos_v), max(min(pos_v + b2.shape[0], b1.shape[0]), 0))
                h_range1 = slice(max(0, pos_h), max(min(pos_h + b2.shape[1], b1.shape[1]), 0))

                v_range2 = slice(max(0, -pos_v), min(-pos_v + b1.shape[0], b2.shape[0]))
                h_range2 = slice(max(0, -pos_h), min(-pos_h + b1.shape[1], b2.shape[1]))

                b1[v_range1, h_range1] += b2[v_range2, h_range2]


                They're added in-place, but you could also create a new array. I might have missed some corner cases, though, but it seems to work fine.






                share|improve this answer















                You just have to find the overlapping range, and then add the arrays using slicing.



                b1 = np.zeros((4,5))
                b2 = np.ones((4,3))
                pos_v, pos_h = 2, 3 # offset
                v_range1 = slice(max(0, pos_v), max(min(pos_v + b2.shape[0], b1.shape[0]), 0))
                h_range1 = slice(max(0, pos_h), max(min(pos_h + b2.shape[1], b1.shape[1]), 0))

                v_range2 = slice(max(0, -pos_v), min(-pos_v + b1.shape[0], b2.shape[0]))
                h_range2 = slice(max(0, -pos_h), min(-pos_h + b1.shape[1], b2.shape[1]))

                b1[v_range1, h_range1] += b2[v_range2, h_range2]


                They're added in-place, but you could also create a new array. I might have missed some corner cases, though, but it seems to work fine.







                share|improve this answer














                share|improve this answer



                share|improve this answer








                edited Mar 28 '12 at 17:54

























                answered Mar 27 '12 at 10:12









                jorgecajorgeca

                4,37411834




                4,37411834













                • I ended up doing something very similar to this. The ability to create slice objects is really great, thanks for that!

                  – fraxel
                  Mar 27 '12 at 12:06











                • I think the v_range1 and h_range1 code is missing a final closing ')'.

                  – David Poole
                  Mar 28 '12 at 15:03











                • Thanks! I just fixed that.

                  – jorgeca
                  Mar 28 '12 at 17:58



















                • I ended up doing something very similar to this. The ability to create slice objects is really great, thanks for that!

                  – fraxel
                  Mar 27 '12 at 12:06











                • I think the v_range1 and h_range1 code is missing a final closing ')'.

                  – David Poole
                  Mar 28 '12 at 15:03











                • Thanks! I just fixed that.

                  – jorgeca
                  Mar 28 '12 at 17:58

















                I ended up doing something very similar to this. The ability to create slice objects is really great, thanks for that!

                – fraxel
                Mar 27 '12 at 12:06





                I ended up doing something very similar to this. The ability to create slice objects is really great, thanks for that!

                – fraxel
                Mar 27 '12 at 12:06













                I think the v_range1 and h_range1 code is missing a final closing ')'.

                – David Poole
                Mar 28 '12 at 15:03





                I think the v_range1 and h_range1 code is missing a final closing ')'.

                – David Poole
                Mar 28 '12 at 15:03













                Thanks! I just fixed that.

                – jorgeca
                Mar 28 '12 at 17:58





                Thanks! I just fixed that.

                – jorgeca
                Mar 28 '12 at 17:58













                14














                An easy solution that looks like MATLAB solution is:



                import numpy as np

                block1 = np.zeros((5,4))
                block2 = np.ones((3,2))

                block1[1:4,2:4] += block2 # use array slicing

                print(block1)

                [[0. 0. 0. 0.]
                [0. 0. 1. 1.]
                [0. 0. 1. 1.]
                [0. 0. 1. 1.]
                [0. 0. 0. 0.]]




                So package it as a reusable function:



                import numpy as np

                def addAtPos(mat1, mat2, xypos):
                """
                Add two matrices of different sizes in place, offset by xy coordinates
                Usage:
                - mat1: base matrix
                - mat2: add this matrix to mat1
                - xypos: tuple (x,y) containing coordinates
                """
                x, y = xypos
                ysize, xsize = mat2.shape
                xmax, ymax = (x + xsize), (y + ysize)
                mat1[y:ymax, x:xmax] += mat2
                return mat1

                block1 = np.zeros((5,4))
                block2 = np.ones((3,2))
                pos = (2,1)
                print(addAtPos(block1, block2, pos))

                [[0. 0. 0. 0.]
                [0. 0. 1. 1.]
                [0. 0. 1. 1.]
                [0. 0. 1. 1.]
                [0. 0. 0. 0.]]





                share|improve this answer





















                • 1





                  This is looking good,and much more readable. But if some of block_2 falls outside block_1 it fails. Easy to fix of course.

                  – fraxel
                  Mar 27 '12 at 9:45











                • @fraxel Yeah, you can always add size checking if needed ;)

                  – EwyynTomato
                  Mar 27 '12 at 9:52
















                14














                An easy solution that looks like MATLAB solution is:



                import numpy as np

                block1 = np.zeros((5,4))
                block2 = np.ones((3,2))

                block1[1:4,2:4] += block2 # use array slicing

                print(block1)

                [[0. 0. 0. 0.]
                [0. 0. 1. 1.]
                [0. 0. 1. 1.]
                [0. 0. 1. 1.]
                [0. 0. 0. 0.]]




                So package it as a reusable function:



                import numpy as np

                def addAtPos(mat1, mat2, xypos):
                """
                Add two matrices of different sizes in place, offset by xy coordinates
                Usage:
                - mat1: base matrix
                - mat2: add this matrix to mat1
                - xypos: tuple (x,y) containing coordinates
                """
                x, y = xypos
                ysize, xsize = mat2.shape
                xmax, ymax = (x + xsize), (y + ysize)
                mat1[y:ymax, x:xmax] += mat2
                return mat1

                block1 = np.zeros((5,4))
                block2 = np.ones((3,2))
                pos = (2,1)
                print(addAtPos(block1, block2, pos))

                [[0. 0. 0. 0.]
                [0. 0. 1. 1.]
                [0. 0. 1. 1.]
                [0. 0. 1. 1.]
                [0. 0. 0. 0.]]





                share|improve this answer





















                • 1





                  This is looking good,and much more readable. But if some of block_2 falls outside block_1 it fails. Easy to fix of course.

                  – fraxel
                  Mar 27 '12 at 9:45











                • @fraxel Yeah, you can always add size checking if needed ;)

                  – EwyynTomato
                  Mar 27 '12 at 9:52














                14












                14








                14







                An easy solution that looks like MATLAB solution is:



                import numpy as np

                block1 = np.zeros((5,4))
                block2 = np.ones((3,2))

                block1[1:4,2:4] += block2 # use array slicing

                print(block1)

                [[0. 0. 0. 0.]
                [0. 0. 1. 1.]
                [0. 0. 1. 1.]
                [0. 0. 1. 1.]
                [0. 0. 0. 0.]]




                So package it as a reusable function:



                import numpy as np

                def addAtPos(mat1, mat2, xypos):
                """
                Add two matrices of different sizes in place, offset by xy coordinates
                Usage:
                - mat1: base matrix
                - mat2: add this matrix to mat1
                - xypos: tuple (x,y) containing coordinates
                """
                x, y = xypos
                ysize, xsize = mat2.shape
                xmax, ymax = (x + xsize), (y + ysize)
                mat1[y:ymax, x:xmax] += mat2
                return mat1

                block1 = np.zeros((5,4))
                block2 = np.ones((3,2))
                pos = (2,1)
                print(addAtPos(block1, block2, pos))

                [[0. 0. 0. 0.]
                [0. 0. 1. 1.]
                [0. 0. 1. 1.]
                [0. 0. 1. 1.]
                [0. 0. 0. 0.]]





                share|improve this answer















                An easy solution that looks like MATLAB solution is:



                import numpy as np

                block1 = np.zeros((5,4))
                block2 = np.ones((3,2))

                block1[1:4,2:4] += block2 # use array slicing

                print(block1)

                [[0. 0. 0. 0.]
                [0. 0. 1. 1.]
                [0. 0. 1. 1.]
                [0. 0. 1. 1.]
                [0. 0. 0. 0.]]




                So package it as a reusable function:



                import numpy as np

                def addAtPos(mat1, mat2, xypos):
                """
                Add two matrices of different sizes in place, offset by xy coordinates
                Usage:
                - mat1: base matrix
                - mat2: add this matrix to mat1
                - xypos: tuple (x,y) containing coordinates
                """
                x, y = xypos
                ysize, xsize = mat2.shape
                xmax, ymax = (x + xsize), (y + ysize)
                mat1[y:ymax, x:xmax] += mat2
                return mat1

                block1 = np.zeros((5,4))
                block2 = np.ones((3,2))
                pos = (2,1)
                print(addAtPos(block1, block2, pos))

                [[0. 0. 0. 0.]
                [0. 0. 1. 1.]
                [0. 0. 1. 1.]
                [0. 0. 1. 1.]
                [0. 0. 0. 0.]]






                share|improve this answer














                share|improve this answer



                share|improve this answer








                edited May 31 '18 at 6:17









                Brian Burns

                7,12254646




                7,12254646










                answered Mar 27 '12 at 9:27









                EwyynTomatoEwyynTomato

                2,72412133




                2,72412133








                • 1





                  This is looking good,and much more readable. But if some of block_2 falls outside block_1 it fails. Easy to fix of course.

                  – fraxel
                  Mar 27 '12 at 9:45











                • @fraxel Yeah, you can always add size checking if needed ;)

                  – EwyynTomato
                  Mar 27 '12 at 9:52














                • 1





                  This is looking good,and much more readable. But if some of block_2 falls outside block_1 it fails. Easy to fix of course.

                  – fraxel
                  Mar 27 '12 at 9:45











                • @fraxel Yeah, you can always add size checking if needed ;)

                  – EwyynTomato
                  Mar 27 '12 at 9:52








                1




                1





                This is looking good,and much more readable. But if some of block_2 falls outside block_1 it fails. Easy to fix of course.

                – fraxel
                Mar 27 '12 at 9:45





                This is looking good,and much more readable. But if some of block_2 falls outside block_1 it fails. Easy to fix of course.

                – fraxel
                Mar 27 '12 at 9:45













                @fraxel Yeah, you can always add size checking if needed ;)

                – EwyynTomato
                Mar 27 '12 at 9:52





                @fraxel Yeah, you can always add size checking if needed ;)

                – EwyynTomato
                Mar 27 '12 at 9:52











                2














                This is great, and here's how to extend the addition to a 3D matrix by adding a few lines to jorgeca's code:



                import numpy as np

                #two 3d arrays, of different size.
                b1 = np.zeros((5,5,5), dtype=np.int) # a 5x5x5 matrix of zeroes
                b2 = np.ones((3,3,3), dtype=np.int) # a 3x3x3 matrix of ones

                pos_v, pos_h, pos_z = 2, 2, 2 # a 3d offset -> to plonk b2 in the corner of b1

                v_range1 = slice(max(0, pos_v), max(min(pos_v + b2.shape[0], b1.shape[0]), 0))
                h_range1 = slice(max(0, pos_h), max(min(pos_h + b2.shape[1], b1.shape[1]), 0))
                z_range1 = slice(max(0, pos_z), max(min(pos_z + b2.shape[2], b1.shape[2]), 0))

                v_range2 = slice(max(0, -pos_v), min(-pos_v + b1.shape[0], b2.shape[0]))
                h_range2 = slice(max(0, -pos_h), min(-pos_h + b1.shape[1], b2.shape[1]))
                z_range2 = slice(max(0, -pos_z), min(-pos_z + b1.shape[2], b2.shape[2]))

                b1[v_range1, h_range1, z_range1] += b2[v_range2, h_range2, z_range2]


                This might help someone who wants to do the same in 3d (like me).






                share|improve this answer




























                  2














                  This is great, and here's how to extend the addition to a 3D matrix by adding a few lines to jorgeca's code:



                  import numpy as np

                  #two 3d arrays, of different size.
                  b1 = np.zeros((5,5,5), dtype=np.int) # a 5x5x5 matrix of zeroes
                  b2 = np.ones((3,3,3), dtype=np.int) # a 3x3x3 matrix of ones

                  pos_v, pos_h, pos_z = 2, 2, 2 # a 3d offset -> to plonk b2 in the corner of b1

                  v_range1 = slice(max(0, pos_v), max(min(pos_v + b2.shape[0], b1.shape[0]), 0))
                  h_range1 = slice(max(0, pos_h), max(min(pos_h + b2.shape[1], b1.shape[1]), 0))
                  z_range1 = slice(max(0, pos_z), max(min(pos_z + b2.shape[2], b1.shape[2]), 0))

                  v_range2 = slice(max(0, -pos_v), min(-pos_v + b1.shape[0], b2.shape[0]))
                  h_range2 = slice(max(0, -pos_h), min(-pos_h + b1.shape[1], b2.shape[1]))
                  z_range2 = slice(max(0, -pos_z), min(-pos_z + b1.shape[2], b2.shape[2]))

                  b1[v_range1, h_range1, z_range1] += b2[v_range2, h_range2, z_range2]


                  This might help someone who wants to do the same in 3d (like me).






                  share|improve this answer


























                    2












                    2








                    2







                    This is great, and here's how to extend the addition to a 3D matrix by adding a few lines to jorgeca's code:



                    import numpy as np

                    #two 3d arrays, of different size.
                    b1 = np.zeros((5,5,5), dtype=np.int) # a 5x5x5 matrix of zeroes
                    b2 = np.ones((3,3,3), dtype=np.int) # a 3x3x3 matrix of ones

                    pos_v, pos_h, pos_z = 2, 2, 2 # a 3d offset -> to plonk b2 in the corner of b1

                    v_range1 = slice(max(0, pos_v), max(min(pos_v + b2.shape[0], b1.shape[0]), 0))
                    h_range1 = slice(max(0, pos_h), max(min(pos_h + b2.shape[1], b1.shape[1]), 0))
                    z_range1 = slice(max(0, pos_z), max(min(pos_z + b2.shape[2], b1.shape[2]), 0))

                    v_range2 = slice(max(0, -pos_v), min(-pos_v + b1.shape[0], b2.shape[0]))
                    h_range2 = slice(max(0, -pos_h), min(-pos_h + b1.shape[1], b2.shape[1]))
                    z_range2 = slice(max(0, -pos_z), min(-pos_z + b1.shape[2], b2.shape[2]))

                    b1[v_range1, h_range1, z_range1] += b2[v_range2, h_range2, z_range2]


                    This might help someone who wants to do the same in 3d (like me).






                    share|improve this answer













                    This is great, and here's how to extend the addition to a 3D matrix by adding a few lines to jorgeca's code:



                    import numpy as np

                    #two 3d arrays, of different size.
                    b1 = np.zeros((5,5,5), dtype=np.int) # a 5x5x5 matrix of zeroes
                    b2 = np.ones((3,3,3), dtype=np.int) # a 3x3x3 matrix of ones

                    pos_v, pos_h, pos_z = 2, 2, 2 # a 3d offset -> to plonk b2 in the corner of b1

                    v_range1 = slice(max(0, pos_v), max(min(pos_v + b2.shape[0], b1.shape[0]), 0))
                    h_range1 = slice(max(0, pos_h), max(min(pos_h + b2.shape[1], b1.shape[1]), 0))
                    z_range1 = slice(max(0, pos_z), max(min(pos_z + b2.shape[2], b1.shape[2]), 0))

                    v_range2 = slice(max(0, -pos_v), min(-pos_v + b1.shape[0], b2.shape[0]))
                    h_range2 = slice(max(0, -pos_h), min(-pos_h + b1.shape[1], b2.shape[1]))
                    z_range2 = slice(max(0, -pos_z), min(-pos_z + b1.shape[2], b2.shape[2]))

                    b1[v_range1, h_range1, z_range1] += b2[v_range2, h_range2, z_range2]


                    This might help someone who wants to do the same in 3d (like me).







                    share|improve this answer












                    share|improve this answer



                    share|improve this answer










                    answered Sep 2 '14 at 22:46









                    kabammikabammi

                    10512




                    10512























                        1














                        I'm sure there is a fast NumPy way to do this, but there is a more efficient way to do it even in normal Python:



                        block_1 = [ [ 0, 0, 0, 0, 0],
                        [ 0, 0, 0, 0, 0],
                        [ 0, 0, 0, 0, 0],
                        [ 0, 0, 0, 0, 0]]

                        block_2 = [ [ 1, 1, 1],
                        [ 1, 1, 1],
                        [ 1, 1, 1],
                        [ 1, 1, 1]]

                        pos = (1, 1)

                        x, y = pos

                        # width of the rows in block_2
                        length = len(block_2[0])

                        # skip the first y rows
                        for row_1, row_2 in zip(block_1[y:], block_2):
                        # set length elements offset by x to the sum.
                        row_1[x:length + x] = map(sum, zip(row_2, row_1[x:length + x]))

                        print 'n'.join(' '.join(map(str, row)) for row in block_1)

                        """
                        0 0 0 0 0
                        0 1 1 1 0
                        0 1 1 1 0
                        0 1 1 1 0
                        """





                        share|improve this answer




























                          1














                          I'm sure there is a fast NumPy way to do this, but there is a more efficient way to do it even in normal Python:



                          block_1 = [ [ 0, 0, 0, 0, 0],
                          [ 0, 0, 0, 0, 0],
                          [ 0, 0, 0, 0, 0],
                          [ 0, 0, 0, 0, 0]]

                          block_2 = [ [ 1, 1, 1],
                          [ 1, 1, 1],
                          [ 1, 1, 1],
                          [ 1, 1, 1]]

                          pos = (1, 1)

                          x, y = pos

                          # width of the rows in block_2
                          length = len(block_2[0])

                          # skip the first y rows
                          for row_1, row_2 in zip(block_1[y:], block_2):
                          # set length elements offset by x to the sum.
                          row_1[x:length + x] = map(sum, zip(row_2, row_1[x:length + x]))

                          print 'n'.join(' '.join(map(str, row)) for row in block_1)

                          """
                          0 0 0 0 0
                          0 1 1 1 0
                          0 1 1 1 0
                          0 1 1 1 0
                          """





                          share|improve this answer


























                            1












                            1








                            1







                            I'm sure there is a fast NumPy way to do this, but there is a more efficient way to do it even in normal Python:



                            block_1 = [ [ 0, 0, 0, 0, 0],
                            [ 0, 0, 0, 0, 0],
                            [ 0, 0, 0, 0, 0],
                            [ 0, 0, 0, 0, 0]]

                            block_2 = [ [ 1, 1, 1],
                            [ 1, 1, 1],
                            [ 1, 1, 1],
                            [ 1, 1, 1]]

                            pos = (1, 1)

                            x, y = pos

                            # width of the rows in block_2
                            length = len(block_2[0])

                            # skip the first y rows
                            for row_1, row_2 in zip(block_1[y:], block_2):
                            # set length elements offset by x to the sum.
                            row_1[x:length + x] = map(sum, zip(row_2, row_1[x:length + x]))

                            print 'n'.join(' '.join(map(str, row)) for row in block_1)

                            """
                            0 0 0 0 0
                            0 1 1 1 0
                            0 1 1 1 0
                            0 1 1 1 0
                            """





                            share|improve this answer













                            I'm sure there is a fast NumPy way to do this, but there is a more efficient way to do it even in normal Python:



                            block_1 = [ [ 0, 0, 0, 0, 0],
                            [ 0, 0, 0, 0, 0],
                            [ 0, 0, 0, 0, 0],
                            [ 0, 0, 0, 0, 0]]

                            block_2 = [ [ 1, 1, 1],
                            [ 1, 1, 1],
                            [ 1, 1, 1],
                            [ 1, 1, 1]]

                            pos = (1, 1)

                            x, y = pos

                            # width of the rows in block_2
                            length = len(block_2[0])

                            # skip the first y rows
                            for row_1, row_2 in zip(block_1[y:], block_2):
                            # set length elements offset by x to the sum.
                            row_1[x:length + x] = map(sum, zip(row_2, row_1[x:length + x]))

                            print 'n'.join(' '.join(map(str, row)) for row in block_1)

                            """
                            0 0 0 0 0
                            0 1 1 1 0
                            0 1 1 1 0
                            0 1 1 1 0
                            """






                            share|improve this answer












                            share|improve this answer



                            share|improve this answer










                            answered Mar 27 '12 at 9:26









                            agfagf

                            117k28230209




                            117k28230209























                                1














                                Here's @jorgeca's great code as a function, with some tests - I expanded the slices to try to make it a little more readable:



                                import numpy as np


                                def addAtPos(matrix1, matrix2, xypos, inPlace=False):
                                """
                                Add matrix2 into matrix1 at position xypos (x,y), in-place or in new matrix.
                                Handles matrix2 going off edges of matrix1.
                                """

                                x, y = xypos
                                h1, w1 = matrix1.shape
                                h2, w2 = matrix2.shape

                                # get slice ranges for matrix1
                                x1min = max(0, x)
                                y1min = max(0, y)
                                x1max = max(min(x + w2, w1), 0)
                                y1max = max(min(y + h2, h1), 0)

                                # get slice ranges for matrix2
                                x2min = max(0, -x)
                                y2min = max(0, -y)
                                x2max = min(-x + w1, w2)
                                y2max = min(-y + h1, h2)

                                if inPlace:
                                # add matrix2 into matrix1, in place
                                matrix1[y1min:y1max, x1min:x1max] += matrix2[y2min:y2max, x2min:x2max]
                                else:
                                # create and return a new matrix
                                matrix1copy = matrix1.copy()
                                matrix1copy[y1min:y1max, x1min:x1max] += matrix2[y2min:y2max, x2min:x2max]
                                return matrix1copy


                                def test_addAtPos():

                                matrix1 = np.zeros((2,2))
                                matrix2 = np.ones((2,2))

                                test(addAtPos(matrix1, matrix2, ( 0, 0)), [[1,1],[1,1]])
                                test(addAtPos(matrix1, matrix2, ( 2, 2)), [[0,0],[0,0]])
                                test(addAtPos(matrix1, matrix2, (-1,-1)), [[1,0],[0,0]])
                                test(addAtPos(matrix1, matrix2, ( 1,-1)), [[0,1],[0,0]])
                                test(addAtPos(matrix1, matrix2, ( 1, 1)), [[0,0],[0,1]])
                                test(addAtPos(matrix1, matrix2, (-1, 1)), [[0,0],[1,0]])


                                def test(actual, expected, message=''):
                                "Compare actual and expected values and print OK or FAIL"
                                passed = (actual == expected)
                                if type(passed) == np.ndarray:
                                passed = passed.all()
                                actual = str(actual).replace('n', '')
                                expected = str(expected).replace('n', '')
                                if passed:
                                print('[OK] ', message, actual)
                                else:
                                print('[FAIL]', message, actual, ' != expected value of', expected)


                                test_addAtPos()


                                Output:



                                [OK]    [[1. 1.] [1. 1.]]
                                [OK] [[0. 0.] [0. 0.]]
                                [OK] [[1. 0.] [0. 0.]]
                                [OK] [[0. 1.] [0. 0.]]
                                [OK] [[0. 0.] [0. 1.]]
                                [OK] [[0. 0.] [1. 0.]]





                                share|improve this answer




























                                  1














                                  Here's @jorgeca's great code as a function, with some tests - I expanded the slices to try to make it a little more readable:



                                  import numpy as np


                                  def addAtPos(matrix1, matrix2, xypos, inPlace=False):
                                  """
                                  Add matrix2 into matrix1 at position xypos (x,y), in-place or in new matrix.
                                  Handles matrix2 going off edges of matrix1.
                                  """

                                  x, y = xypos
                                  h1, w1 = matrix1.shape
                                  h2, w2 = matrix2.shape

                                  # get slice ranges for matrix1
                                  x1min = max(0, x)
                                  y1min = max(0, y)
                                  x1max = max(min(x + w2, w1), 0)
                                  y1max = max(min(y + h2, h1), 0)

                                  # get slice ranges for matrix2
                                  x2min = max(0, -x)
                                  y2min = max(0, -y)
                                  x2max = min(-x + w1, w2)
                                  y2max = min(-y + h1, h2)

                                  if inPlace:
                                  # add matrix2 into matrix1, in place
                                  matrix1[y1min:y1max, x1min:x1max] += matrix2[y2min:y2max, x2min:x2max]
                                  else:
                                  # create and return a new matrix
                                  matrix1copy = matrix1.copy()
                                  matrix1copy[y1min:y1max, x1min:x1max] += matrix2[y2min:y2max, x2min:x2max]
                                  return matrix1copy


                                  def test_addAtPos():

                                  matrix1 = np.zeros((2,2))
                                  matrix2 = np.ones((2,2))

                                  test(addAtPos(matrix1, matrix2, ( 0, 0)), [[1,1],[1,1]])
                                  test(addAtPos(matrix1, matrix2, ( 2, 2)), [[0,0],[0,0]])
                                  test(addAtPos(matrix1, matrix2, (-1,-1)), [[1,0],[0,0]])
                                  test(addAtPos(matrix1, matrix2, ( 1,-1)), [[0,1],[0,0]])
                                  test(addAtPos(matrix1, matrix2, ( 1, 1)), [[0,0],[0,1]])
                                  test(addAtPos(matrix1, matrix2, (-1, 1)), [[0,0],[1,0]])


                                  def test(actual, expected, message=''):
                                  "Compare actual and expected values and print OK or FAIL"
                                  passed = (actual == expected)
                                  if type(passed) == np.ndarray:
                                  passed = passed.all()
                                  actual = str(actual).replace('n', '')
                                  expected = str(expected).replace('n', '')
                                  if passed:
                                  print('[OK] ', message, actual)
                                  else:
                                  print('[FAIL]', message, actual, ' != expected value of', expected)


                                  test_addAtPos()


                                  Output:



                                  [OK]    [[1. 1.] [1. 1.]]
                                  [OK] [[0. 0.] [0. 0.]]
                                  [OK] [[1. 0.] [0. 0.]]
                                  [OK] [[0. 1.] [0. 0.]]
                                  [OK] [[0. 0.] [0. 1.]]
                                  [OK] [[0. 0.] [1. 0.]]





                                  share|improve this answer


























                                    1












                                    1








                                    1







                                    Here's @jorgeca's great code as a function, with some tests - I expanded the slices to try to make it a little more readable:



                                    import numpy as np


                                    def addAtPos(matrix1, matrix2, xypos, inPlace=False):
                                    """
                                    Add matrix2 into matrix1 at position xypos (x,y), in-place or in new matrix.
                                    Handles matrix2 going off edges of matrix1.
                                    """

                                    x, y = xypos
                                    h1, w1 = matrix1.shape
                                    h2, w2 = matrix2.shape

                                    # get slice ranges for matrix1
                                    x1min = max(0, x)
                                    y1min = max(0, y)
                                    x1max = max(min(x + w2, w1), 0)
                                    y1max = max(min(y + h2, h1), 0)

                                    # get slice ranges for matrix2
                                    x2min = max(0, -x)
                                    y2min = max(0, -y)
                                    x2max = min(-x + w1, w2)
                                    y2max = min(-y + h1, h2)

                                    if inPlace:
                                    # add matrix2 into matrix1, in place
                                    matrix1[y1min:y1max, x1min:x1max] += matrix2[y2min:y2max, x2min:x2max]
                                    else:
                                    # create and return a new matrix
                                    matrix1copy = matrix1.copy()
                                    matrix1copy[y1min:y1max, x1min:x1max] += matrix2[y2min:y2max, x2min:x2max]
                                    return matrix1copy


                                    def test_addAtPos():

                                    matrix1 = np.zeros((2,2))
                                    matrix2 = np.ones((2,2))

                                    test(addAtPos(matrix1, matrix2, ( 0, 0)), [[1,1],[1,1]])
                                    test(addAtPos(matrix1, matrix2, ( 2, 2)), [[0,0],[0,0]])
                                    test(addAtPos(matrix1, matrix2, (-1,-1)), [[1,0],[0,0]])
                                    test(addAtPos(matrix1, matrix2, ( 1,-1)), [[0,1],[0,0]])
                                    test(addAtPos(matrix1, matrix2, ( 1, 1)), [[0,0],[0,1]])
                                    test(addAtPos(matrix1, matrix2, (-1, 1)), [[0,0],[1,0]])


                                    def test(actual, expected, message=''):
                                    "Compare actual and expected values and print OK or FAIL"
                                    passed = (actual == expected)
                                    if type(passed) == np.ndarray:
                                    passed = passed.all()
                                    actual = str(actual).replace('n', '')
                                    expected = str(expected).replace('n', '')
                                    if passed:
                                    print('[OK] ', message, actual)
                                    else:
                                    print('[FAIL]', message, actual, ' != expected value of', expected)


                                    test_addAtPos()


                                    Output:



                                    [OK]    [[1. 1.] [1. 1.]]
                                    [OK] [[0. 0.] [0. 0.]]
                                    [OK] [[1. 0.] [0. 0.]]
                                    [OK] [[0. 1.] [0. 0.]]
                                    [OK] [[0. 0.] [0. 1.]]
                                    [OK] [[0. 0.] [1. 0.]]





                                    share|improve this answer













                                    Here's @jorgeca's great code as a function, with some tests - I expanded the slices to try to make it a little more readable:



                                    import numpy as np


                                    def addAtPos(matrix1, matrix2, xypos, inPlace=False):
                                    """
                                    Add matrix2 into matrix1 at position xypos (x,y), in-place or in new matrix.
                                    Handles matrix2 going off edges of matrix1.
                                    """

                                    x, y = xypos
                                    h1, w1 = matrix1.shape
                                    h2, w2 = matrix2.shape

                                    # get slice ranges for matrix1
                                    x1min = max(0, x)
                                    y1min = max(0, y)
                                    x1max = max(min(x + w2, w1), 0)
                                    y1max = max(min(y + h2, h1), 0)

                                    # get slice ranges for matrix2
                                    x2min = max(0, -x)
                                    y2min = max(0, -y)
                                    x2max = min(-x + w1, w2)
                                    y2max = min(-y + h1, h2)

                                    if inPlace:
                                    # add matrix2 into matrix1, in place
                                    matrix1[y1min:y1max, x1min:x1max] += matrix2[y2min:y2max, x2min:x2max]
                                    else:
                                    # create and return a new matrix
                                    matrix1copy = matrix1.copy()
                                    matrix1copy[y1min:y1max, x1min:x1max] += matrix2[y2min:y2max, x2min:x2max]
                                    return matrix1copy


                                    def test_addAtPos():

                                    matrix1 = np.zeros((2,2))
                                    matrix2 = np.ones((2,2))

                                    test(addAtPos(matrix1, matrix2, ( 0, 0)), [[1,1],[1,1]])
                                    test(addAtPos(matrix1, matrix2, ( 2, 2)), [[0,0],[0,0]])
                                    test(addAtPos(matrix1, matrix2, (-1,-1)), [[1,0],[0,0]])
                                    test(addAtPos(matrix1, matrix2, ( 1,-1)), [[0,1],[0,0]])
                                    test(addAtPos(matrix1, matrix2, ( 1, 1)), [[0,0],[0,1]])
                                    test(addAtPos(matrix1, matrix2, (-1, 1)), [[0,0],[1,0]])


                                    def test(actual, expected, message=''):
                                    "Compare actual and expected values and print OK or FAIL"
                                    passed = (actual == expected)
                                    if type(passed) == np.ndarray:
                                    passed = passed.all()
                                    actual = str(actual).replace('n', '')
                                    expected = str(expected).replace('n', '')
                                    if passed:
                                    print('[OK] ', message, actual)
                                    else:
                                    print('[FAIL]', message, actual, ' != expected value of', expected)


                                    test_addAtPos()


                                    Output:



                                    [OK]    [[1. 1.] [1. 1.]]
                                    [OK] [[0. 0.] [0. 0.]]
                                    [OK] [[1. 0.] [0. 0.]]
                                    [OK] [[0. 1.] [0. 0.]]
                                    [OK] [[0. 0.] [0. 1.]]
                                    [OK] [[0. 0.] [1. 0.]]






                                    share|improve this answer












                                    share|improve this answer



                                    share|improve this answer










                                    answered May 31 '18 at 17:38









                                    Brian BurnsBrian Burns

                                    7,12254646




                                    7,12254646






























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