How to start from second index for for-loop

I have this for-loop. I want i in range(nI) to start from the second number in the I list. Could you guide me?

I=[0,1,2,3,4,5,6]

nI=len(I)

for i in range(nI):

    sum=0

    for v in range(nV):

        for j in range(nJ):

            sum=sum+x1[i][j][v]

return sum

edited Jan 1 at 4:26

AI_Learning

3,57721033

asked Dec 4 '18 at 21:29

Mary

134

add a comment |

I have this for-loop. I want i in range(nI) to start from the second number in the I list. Could you guide me?

I=[0,1,2,3,4,5,6]

nI=len(I)

for i in range(nI):

    sum=0

    for v in range(nV):

        for j in range(nJ):

            sum=sum+x1[i][j][v]

return sum

edited Jan 1 at 4:26

AI_Learning

3,57721033

asked Dec 4 '18 at 21:29

Mary

134

add a comment |

I have this for-loop. I want i in range(nI) to start from the second number in the I list. Could you guide me?

I=[0,1,2,3,4,5,6]

nI=len(I)

for i in range(nI):

    sum=0

    for v in range(nV):

        for j in range(nJ):

            sum=sum+x1[i][j][v]

return sum

edited Jan 1 at 4:26

AI_Learning

3,57721033

asked Dec 4 '18 at 21:29

Mary

134

I have this for-loop. I want i in range(nI) to start from the second number in the I list. Could you guide me?

I=[0,1,2,3,4,5,6]

nI=len(I)

for i in range(nI):

    sum=0

    for v in range(nV):

        for j in range(nJ):

            sum=sum+x1[i][j][v]

return sum

python python-3.x numpy

edited Jan 1 at 4:26

AI_Learning

3,57721033

asked Dec 4 '18 at 21:29

Mary

134

edited Jan 1 at 4:26

AI_Learning

3,57721033

asked Dec 4 '18 at 21:29

Mary

134

edited Jan 1 at 4:26

AI_Learning

3,57721033

edited Jan 1 at 4:26

AI_Learning

3,57721033

edited Jan 1 at 4:26

AI_Learning

3,57721033

asked Dec 4 '18 at 21:29

Mary

134

asked Dec 4 '18 at 21:29

Mary

134

asked Dec 4 '18 at 21:29

Mary

134

add a comment |

3 Answers
3

active

oldest

votes

First thing is to remember that python uses zero indexing.

You can iterate throught the list except using the range function to get the indexes of the items you want or slices to get the elements.

What I think is becoming confusing here is that in your example, the values and the indexes are the same so to clarify I'll use this list as example:

I = ['a', 'b', 'c', 'd', 'e']

nI = len(I) # 5

The range function will allow you to iterate through the indexes:

for i in range(1, nI):

    print(i)

# Prints:

# 1

# 2

# 3

# 4

If you want to access the values using the range function you should do it like this:

for index in range(1, nI):

    i = I[index]

    print(i)

# Prints:

# b

# c

# d

# e

You can also use array slicing to do that and you don't even need nI. Array slicing returns a new array with your slice.

The slice is done with the_list_reference[start:end:steps] where all three parameters are optional and:
start is the index of the first to be included in the slice
end is the index of the first element to be excluded from the slice
steps is how many steps for each next index starting from (as expected) the start (if steps is 2 and start with 1 it gets every odd index).

Example:

for i in I[1:]:

    print(i)

# Prints:

# b

# c

# d

# e

answered Jan 1 at 5:05

Luiz Ferraz

714

add a comment |

If you want to iterate through a list from a second item, just use range(1, nI) (if nI is the length of the list or so).

for i in range(1, nI):

    sum=0

    for v in range(nV):

        for j in range(nJ):

            sum=sum+x1[i][j][v]

Probaly, a part of your function just lost somewhere, but anyway, in in general range() works like this:

range(start_from, stop_at, step_size)

i. e.

for i in range(2, 7, 2):

    print(i, end=' ')



Out:

2 4 6

Edit

Please, remember: python uses zero indexing, i.e. first element has an index 0, the second - 1 etc.

By default, range starts from 0 and stops at the value of the passed parameter minus one. If there's an explicit start, iteration starts from it's value. If there's a step, it continues while range returns values lesser than stop value.

for i in range(1, 7, 2):

    print(i, end=' ')



Out: 

1 3 5  # there's no 7!

Detailed description of range build-in is here.

edited Dec 4 '18 at 21:47

answered Dec 4 '18 at 21:38

Mikhail Stepanov

1,5693812

My range is I=5 but I want to skip 1 from this range and start from i=2 in this range

– Mary
Dec 4 '18 at 21:47

Can you edit your post and add the missing part of your code snippet? Guess it's possible to solve it without range just with slices.

– Mikhail Stepanov
Dec 4 '18 at 21:53

I did. I want i starts from 1 in my list. I don't want 0 for my for-loop

– Mary
Dec 4 '18 at 22:04

add a comment |

Range starts from the 0 index if not otherwise specified. You want to use something like

for i in range(1,nI):

    ...

answered Dec 4 '18 at 21:36

Jack Moody

722723

My range is 5 but I want to skip 1 from this range and start from i=2 in this range

– Mary
Dec 4 '18 at 21:47

So you want to get the second through fifth items in your list?

– Jack Moody
Dec 4 '18 at 21:51

I want my for loop get the index of the second value in the list and do the iteration to end

– Mary
Dec 4 '18 at 21:56

I want something like this: for i+1 in range(n)

– Mary
Dec 4 '18 at 21:57

Ok. Does the solution I gave work for you?

– Jack Moody
Dec 4 '18 at 21:58

|
show 1 more comment

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3 Answers
3

active

oldest

votes

3 Answers
3

active

oldest

votes

First thing is to remember that python uses zero indexing.

You can iterate throught the list except using the range function to get the indexes of the items you want or slices to get the elements.

What I think is becoming confusing here is that in your example, the values and the indexes are the same so to clarify I'll use this list as example:

I = ['a', 'b', 'c', 'd', 'e']

nI = len(I) # 5

The range function will allow you to iterate through the indexes:

for i in range(1, nI):

    print(i)

# Prints:

# 1

# 2

# 3

# 4

If you want to access the values using the range function you should do it like this:

for index in range(1, nI):

    i = I[index]

    print(i)

# Prints:

# b

# c

# d

# e

for i in I[1:]:

    print(i)

# Prints:

# b

# c

# d

# e

answered Jan 1 at 5:05

Luiz Ferraz

714

add a comment |

First thing is to remember that python uses zero indexing.

You can iterate throught the list except using the range function to get the indexes of the items you want or slices to get the elements.

What I think is becoming confusing here is that in your example, the values and the indexes are the same so to clarify I'll use this list as example:

I = ['a', 'b', 'c', 'd', 'e']

nI = len(I) # 5

The range function will allow you to iterate through the indexes:

for i in range(1, nI):

    print(i)

# Prints:

# 1

# 2

# 3

# 4

If you want to access the values using the range function you should do it like this:

for index in range(1, nI):

    i = I[index]

    print(i)

# Prints:

# b

# c

# d

# e

for i in I[1:]:

    print(i)

# Prints:

# b

# c

# d

# e

answered Jan 1 at 5:05

Luiz Ferraz

714

add a comment |

First thing is to remember that python uses zero indexing.

You can iterate throught the list except using the range function to get the indexes of the items you want or slices to get the elements.

What I think is becoming confusing here is that in your example, the values and the indexes are the same so to clarify I'll use this list as example:

I = ['a', 'b', 'c', 'd', 'e']

nI = len(I) # 5

The range function will allow you to iterate through the indexes:

for i in range(1, nI):

    print(i)

# Prints:

# 1

# 2

# 3

# 4

If you want to access the values using the range function you should do it like this:

for index in range(1, nI):

    i = I[index]

    print(i)

# Prints:

# b

# c

# d

# e

for i in I[1:]:

    print(i)

# Prints:

# b

# c

# d

# e

answered Jan 1 at 5:05

Luiz Ferraz

714

First thing is to remember that python uses zero indexing.

You can iterate throught the list except using the range function to get the indexes of the items you want or slices to get the elements.

What I think is becoming confusing here is that in your example, the values and the indexes are the same so to clarify I'll use this list as example:

I = ['a', 'b', 'c', 'd', 'e']

nI = len(I) # 5

The range function will allow you to iterate through the indexes:

for i in range(1, nI):

    print(i)

# Prints:

# 1

# 2

# 3

# 4

If you want to access the values using the range function you should do it like this:

for index in range(1, nI):

    i = I[index]

    print(i)

# Prints:

# b

# c

# d

# e

for i in I[1:]:

    print(i)

# Prints:

# b

# c

# d

# e

answered Jan 1 at 5:05

Luiz Ferraz

714

answered Jan 1 at 5:05

Luiz Ferraz

714

answered Jan 1 at 5:05

Luiz Ferraz

714

answered Jan 1 at 5:05

Luiz Ferraz

714

add a comment |

If you want to iterate through a list from a second item, just use range(1, nI) (if nI is the length of the list or so).

for i in range(1, nI):

    sum=0

    for v in range(nV):

        for j in range(nJ):

            sum=sum+x1[i][j][v]

Probaly, a part of your function just lost somewhere, but anyway, in in general range() works like this:

range(start_from, stop_at, step_size)

i. e.

for i in range(2, 7, 2):

    print(i, end=' ')



Out:

2 4 6

Edit

Please, remember: python uses zero indexing, i.e. first element has an index 0, the second - 1 etc.

for i in range(1, 7, 2):

    print(i, end=' ')



Out: 

1 3 5  # there's no 7!

Detailed description of range build-in is here.

edited Dec 4 '18 at 21:47

answered Dec 4 '18 at 21:38

Mikhail Stepanov

1,5693812

My range is I=5 but I want to skip 1 from this range and start from i=2 in this range

– Mary
Dec 4 '18 at 21:47

Can you edit your post and add the missing part of your code snippet? Guess it's possible to solve it without range just with slices.

– Mikhail Stepanov
Dec 4 '18 at 21:53

I did. I want i starts from 1 in my list. I don't want 0 for my for-loop

– Mary
Dec 4 '18 at 22:04

add a comment |

If you want to iterate through a list from a second item, just use range(1, nI) (if nI is the length of the list or so).

for i in range(1, nI):

    sum=0

    for v in range(nV):

        for j in range(nJ):

            sum=sum+x1[i][j][v]

Probaly, a part of your function just lost somewhere, but anyway, in in general range() works like this:

range(start_from, stop_at, step_size)

i. e.

for i in range(2, 7, 2):

    print(i, end=' ')



Out:

2 4 6

Edit

Please, remember: python uses zero indexing, i.e. first element has an index 0, the second - 1 etc.

for i in range(1, 7, 2):

    print(i, end=' ')



Out: 

1 3 5  # there's no 7!

Detailed description of range build-in is here.

edited Dec 4 '18 at 21:47

answered Dec 4 '18 at 21:38

Mikhail Stepanov

1,5693812

My range is I=5 but I want to skip 1 from this range and start from i=2 in this range

– Mary
Dec 4 '18 at 21:47

Can you edit your post and add the missing part of your code snippet? Guess it's possible to solve it without range just with slices.

– Mikhail Stepanov
Dec 4 '18 at 21:53

I did. I want i starts from 1 in my list. I don't want 0 for my for-loop

– Mary
Dec 4 '18 at 22:04

add a comment |

If you want to iterate through a list from a second item, just use range(1, nI) (if nI is the length of the list or so).

for i in range(1, nI):

    sum=0

    for v in range(nV):

        for j in range(nJ):

            sum=sum+x1[i][j][v]

Probaly, a part of your function just lost somewhere, but anyway, in in general range() works like this:

range(start_from, stop_at, step_size)

i. e.

for i in range(2, 7, 2):

    print(i, end=' ')



Out:

2 4 6

Edit

Please, remember: python uses zero indexing, i.e. first element has an index 0, the second - 1 etc.

for i in range(1, 7, 2):

    print(i, end=' ')



Out: 

1 3 5  # there's no 7!

Detailed description of range build-in is here.

edited Dec 4 '18 at 21:47

answered Dec 4 '18 at 21:38

Mikhail Stepanov

1,5693812

If you want to iterate through a list from a second item, just use range(1, nI) (if nI is the length of the list or so).

for i in range(1, nI):

    sum=0

    for v in range(nV):

        for j in range(nJ):

            sum=sum+x1[i][j][v]

Probaly, a part of your function just lost somewhere, but anyway, in in general range() works like this:

range(start_from, stop_at, step_size)

i. e.

for i in range(2, 7, 2):

    print(i, end=' ')



Out:

2 4 6

Edit

Please, remember: python uses zero indexing, i.e. first element has an index 0, the second - 1 etc.

for i in range(1, 7, 2):

    print(i, end=' ')



Out: 

1 3 5  # there's no 7!

Detailed description of range build-in is here.

edited Dec 4 '18 at 21:47

answered Dec 4 '18 at 21:38

Mikhail Stepanov

1,5693812

edited Dec 4 '18 at 21:47

answered Dec 4 '18 at 21:38

Mikhail Stepanov

1,5693812

answered Dec 4 '18 at 21:38

Mikhail Stepanov

1,5693812

answered Dec 4 '18 at 21:38

Mikhail Stepanov

1,5693812

My range is I=5 but I want to skip 1 from this range and start from i=2 in this range

– Mary
Dec 4 '18 at 21:47

Can you edit your post and add the missing part of your code snippet? Guess it's possible to solve it without range just with slices.

– Mikhail Stepanov
Dec 4 '18 at 21:53

I did. I want i starts from 1 in my list. I don't want 0 for my for-loop

– Mary
Dec 4 '18 at 22:04

add a comment |

My range is I=5 but I want to skip 1 from this range and start from i=2 in this range

– Mary
Dec 4 '18 at 21:47

Can you edit your post and add the missing part of your code snippet? Guess it's possible to solve it without range just with slices.

– Mikhail Stepanov
Dec 4 '18 at 21:53

I did. I want i starts from 1 in my list. I don't want 0 for my for-loop

– Mary
Dec 4 '18 at 22:04

My range is I=5 but I want to skip 1 from this range and start from i=2 in this range

– Mary
Dec 4 '18 at 21:47

Can you edit your post and add the missing part of your code snippet? Guess it's possible to solve it without range just with slices.

– Mikhail Stepanov
Dec 4 '18 at 21:53

I did. I want i starts from 1 in my list. I don't want 0 for my for-loop

– Mary
Dec 4 '18 at 22:04

add a comment |

Range starts from the 0 index if not otherwise specified. You want to use something like

for i in range(1,nI):

    ...

answered Dec 4 '18 at 21:36

Jack Moody

722723

My range is 5 but I want to skip 1 from this range and start from i=2 in this range

– Mary
Dec 4 '18 at 21:47

So you want to get the second through fifth items in your list?

– Jack Moody
Dec 4 '18 at 21:51

I want my for loop get the index of the second value in the list and do the iteration to end

– Mary
Dec 4 '18 at 21:56

I want something like this: for i+1 in range(n)

– Mary
Dec 4 '18 at 21:57

Ok. Does the solution I gave work for you?

– Jack Moody
Dec 4 '18 at 21:58

|
show 1 more comment

Range starts from the 0 index if not otherwise specified. You want to use something like

for i in range(1,nI):

    ...

answered Dec 4 '18 at 21:36

Jack Moody

722723

My range is 5 but I want to skip 1 from this range and start from i=2 in this range

– Mary
Dec 4 '18 at 21:47

So you want to get the second through fifth items in your list?

– Jack Moody
Dec 4 '18 at 21:51

I want my for loop get the index of the second value in the list and do the iteration to end

– Mary
Dec 4 '18 at 21:56

I want something like this: for i+1 in range(n)

– Mary
Dec 4 '18 at 21:57

Ok. Does the solution I gave work for you?

– Jack Moody
Dec 4 '18 at 21:58

|
show 1 more comment

Range starts from the 0 index if not otherwise specified. You want to use something like

for i in range(1,nI):

    ...

answered Dec 4 '18 at 21:36

Jack Moody

722723

Range starts from the 0 index if not otherwise specified. You want to use something like

for i in range(1,nI):

    ...

answered Dec 4 '18 at 21:36

Jack Moody

722723

answered Dec 4 '18 at 21:36

Jack Moody

722723

answered Dec 4 '18 at 21:36

Jack Moody

722723

answered Dec 4 '18 at 21:36

Jack Moody

722723

My range is 5 but I want to skip 1 from this range and start from i=2 in this range

– Mary
Dec 4 '18 at 21:47

So you want to get the second through fifth items in your list?

– Jack Moody
Dec 4 '18 at 21:51

I want my for loop get the index of the second value in the list and do the iteration to end

– Mary
Dec 4 '18 at 21:56

I want something like this: for i+1 in range(n)

– Mary
Dec 4 '18 at 21:57

Ok. Does the solution I gave work for you?

– Jack Moody
Dec 4 '18 at 21:58

|
show 1 more comment

My range is 5 but I want to skip 1 from this range and start from i=2 in this range

– Mary
Dec 4 '18 at 21:47

So you want to get the second through fifth items in your list?

– Jack Moody
Dec 4 '18 at 21:51

I want my for loop get the index of the second value in the list and do the iteration to end

– Mary
Dec 4 '18 at 21:56

I want something like this: for i+1 in range(n)

– Mary
Dec 4 '18 at 21:57

Ok. Does the solution I gave work for you?

– Jack Moody
Dec 4 '18 at 21:58

My range is 5 but I want to skip 1 from this range and start from i=2 in this range

– Mary
Dec 4 '18 at 21:47

So you want to get the second through fifth items in your list?

– Jack Moody
Dec 4 '18 at 21:51

I want my for loop get the index of the second value in the list and do the iteration to end

– Mary
Dec 4 '18 at 21:56

I want something like this: for i+1 in range(n)

– Mary
Dec 4 '18 at 21:57

Ok. Does the solution I gave work for you?

– Jack Moody
Dec 4 '18 at 21:58

|
show 1 more comment

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