find the list with the minimum size over a list of list

I have a list of list and i want to return the list that have the min size using java Stream.

Here what i tried:

import java.util.ArrayList;

import java.util.Arrays;

import java.util.stream.Collectors;

import java.util.stream.IntStream;



public class Example {

   public static void main( String args )  {

         ArrayList<Integer> list1 = new ArrayList<>();

         list1.add(0);list1.add(2);list1.add(3);



         ArrayList<Integer> list2 = new ArrayList<>();

         list2.add(0);list2.add(2);list2.add(3);list2.add(4);



         System.out.println( getTheMinList(list1,list2).size());    

   }



   public static ArrayList<Integer> getTheMinList(ArrayList<Integer>... lists) {

         return Arrays.stream(lists)

                      .map(list->list.size())

                      /*here i stoped*/

                ;

   }

}

The program should print 3 because the first list has the minimum size.

Note that I can't change the signature of the getTheMinList(). Could anyone please give me a hint?

edited Nov 20 '18 at 19:56

Stefan Zobel

2,44031828

asked Nov 20 '18 at 16:57

zak zak

496214

What's wrong with a simple if-else?

– Nicholas K
Nov 20 '18 at 16:59

@NicholasK i call the getTheMinList many times with different size arguments, what i wrote was just a tiny example.

– zak zak
Nov 20 '18 at 17:41

add a comment |

I have a list of list and i want to return the list that have the min size using java Stream.

Here what i tried:

import java.util.ArrayList;

import java.util.Arrays;

import java.util.stream.Collectors;

import java.util.stream.IntStream;



public class Example {

   public static void main( String args )  {

         ArrayList<Integer> list1 = new ArrayList<>();

         list1.add(0);list1.add(2);list1.add(3);



         ArrayList<Integer> list2 = new ArrayList<>();

         list2.add(0);list2.add(2);list2.add(3);list2.add(4);



         System.out.println( getTheMinList(list1,list2).size());    

   }



   public static ArrayList<Integer> getTheMinList(ArrayList<Integer>... lists) {

         return Arrays.stream(lists)

                      .map(list->list.size())

                      /*here i stoped*/

                ;

   }

}

The program should print 3 because the first list has the minimum size.

Note that I can't change the signature of the getTheMinList(). Could anyone please give me a hint?

edited Nov 20 '18 at 19:56

Stefan Zobel

2,44031828

asked Nov 20 '18 at 16:57

zak zak

496214

What's wrong with a simple if-else?

– Nicholas K
Nov 20 '18 at 16:59

@NicholasK i call the getTheMinList many times with different size arguments, what i wrote was just a tiny example.

– zak zak
Nov 20 '18 at 17:41

add a comment |

I have a list of list and i want to return the list that have the min size using java Stream.

Here what i tried:

import java.util.ArrayList;

import java.util.Arrays;

import java.util.stream.Collectors;

import java.util.stream.IntStream;



public class Example {

   public static void main( String args )  {

         ArrayList<Integer> list1 = new ArrayList<>();

         list1.add(0);list1.add(2);list1.add(3);



         ArrayList<Integer> list2 = new ArrayList<>();

         list2.add(0);list2.add(2);list2.add(3);list2.add(4);



         System.out.println( getTheMinList(list1,list2).size());    

   }



   public static ArrayList<Integer> getTheMinList(ArrayList<Integer>... lists) {

         return Arrays.stream(lists)

                      .map(list->list.size())

                      /*here i stoped*/

                ;

   }

}

The program should print 3 because the first list has the minimum size.

Note that I can't change the signature of the getTheMinList(). Could anyone please give me a hint?

edited Nov 20 '18 at 19:56

Stefan Zobel

2,44031828

asked Nov 20 '18 at 16:57

zak zak

496214

I have a list of list and i want to return the list that have the min size using java Stream.

Here what i tried:

import java.util.ArrayList;

import java.util.Arrays;

import java.util.stream.Collectors;

import java.util.stream.IntStream;



public class Example {

   public static void main( String args )  {

         ArrayList<Integer> list1 = new ArrayList<>();

         list1.add(0);list1.add(2);list1.add(3);



         ArrayList<Integer> list2 = new ArrayList<>();

         list2.add(0);list2.add(2);list2.add(3);list2.add(4);



         System.out.println( getTheMinList(list1,list2).size());    

   }



   public static ArrayList<Integer> getTheMinList(ArrayList<Integer>... lists) {

         return Arrays.stream(lists)

                      .map(list->list.size())

                      /*here i stoped*/

                ;

   }

}

The program should print 3 because the first list has the minimum size.

Note that I can't change the signature of the getTheMinList(). Could anyone please give me a hint?

java java-stream

edited Nov 20 '18 at 19:56

Stefan Zobel

2,44031828

asked Nov 20 '18 at 16:57

zak zak

496214

edited Nov 20 '18 at 19:56

Stefan Zobel

2,44031828

asked Nov 20 '18 at 16:57

zak zak

496214

edited Nov 20 '18 at 19:56

Stefan Zobel

2,44031828

edited Nov 20 '18 at 19:56

Stefan Zobel

2,44031828

edited Nov 20 '18 at 19:56

Stefan Zobel

2,44031828

asked Nov 20 '18 at 16:57

zak zak

496214

asked Nov 20 '18 at 16:57

zak zak

496214

asked Nov 20 '18 at 16:57

zak zak

496214

What's wrong with a simple if-else?

– Nicholas K
Nov 20 '18 at 16:59

@NicholasK i call the getTheMinList many times with different size arguments, what i wrote was just a tiny example.

– zak zak
Nov 20 '18 at 17:41

add a comment |

What's wrong with a simple if-else?

– Nicholas K
Nov 20 '18 at 16:59

@NicholasK i call the getTheMinList many times with different size arguments, what i wrote was just a tiny example.

– zak zak
Nov 20 '18 at 17:41

What's wrong with a simple if-else?

– Nicholas K
Nov 20 '18 at 16:59

@NicholasK i call the getTheMinList many times with different size arguments, what i wrote was just a tiny example.

– zak zak
Nov 20 '18 at 17:41

add a comment |

2 Answers
2

active

oldest

votes

You can use Stream.min comparing the List.size:

public static List<Integer> getTheMinList(List<Integer>... lists){

    return Arrays.stream(lists)

            .min(Comparator.comparingInt(List::size))

            .orElse(new ArrayList<>());

}

or possibly better if you could get rid of var-args and unchecked assignment

private static List<Integer> getTheMinList(List<List<Integer>> lists){

    return lists.stream()

            .min(Comparator.comparingInt(List::size))

            .orElse(new ArrayList<>());

}

// invoked as

System.out.println(getTheMinList(List.of(list1, list2)).size());

edited Nov 20 '18 at 17:08

answered Nov 20 '18 at 17:03

nullpointer

46.5k1199191

1

Another suggestion: Try programming to an interface.

– nullpointer
Nov 20 '18 at 17:09

Thank you, i use the var arg because i call the getTheMinList many times with different size arguments.

– zak zak
Nov 20 '18 at 17:40

@zakzak List<List<Integer>> can as well accept varying size outer List as an argument if you'd noticed. This means you can call it as getTheMinList(List.of(List.of(0, 2, 3), List.of(0, 2, 3, 4))) and getTheMinList(List.of(List.of(0, 2, 3), List.of(0, 2, 3, 4), List.of(1,2,3))) as well.

– nullpointer
Nov 20 '18 at 17:42

yes but i should send a list of list as argument every time, in my program i send many list as argument, like getTheMinList(l1,l2) ,getTheMinList(l1,l2,l3) ans so on...and i m using only java 8.

– zak zak
Nov 20 '18 at 17:43

1

@zakzak the return type of min is Optional<T> for which you either check for an Optional.empty or can fallback to a default value using Optional.orElse API.

– nullpointer
Nov 20 '18 at 18:11

|
show 2 more comments

Just another idea...

as @NullPointer suggested, I’d make the method take a List<List<Integer>> rather than the varargs.

Given this change you can simply do:

Collections.min(lists, Comparator.comparingInt(List::size));

Short, simple and readable right?

Note that the above will throw a NoSuchElementException upon the collection being empty which may aswell be the expected behaviour you’re wanting but just in case that’s not the the intended behaviour you may want to check for emptiness before the call to min or use the stream approach suggested by @NullPointer which uses the Optional API to return an alternative value if Stream#min returns an empty Optional.

answered Nov 20 '18 at 17:22

Aomine

41.9k74071

thank you, i will review my code.in general every list should be not null before the call.

– zak zak
Nov 20 '18 at 17:47

1

When you stay with varargs, you can still use this solution as simple as return Collections.min(Arrays.asList(lists), Comparator.comparingInt(List::size)); This uses Arrays.asList which creates a lightweight wrapper around the array, allowing to apply the entirety of the Collection API on an existing array…

– Holger
Nov 21 '18 at 8:54

add a comment |

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2 Answers
2

active

oldest

votes

2 Answers
2

active

oldest

votes

You can use Stream.min comparing the List.size:

public static List<Integer> getTheMinList(List<Integer>... lists){

    return Arrays.stream(lists)

            .min(Comparator.comparingInt(List::size))

            .orElse(new ArrayList<>());

}

or possibly better if you could get rid of var-args and unchecked assignment

private static List<Integer> getTheMinList(List<List<Integer>> lists){

    return lists.stream()

            .min(Comparator.comparingInt(List::size))

            .orElse(new ArrayList<>());

}

// invoked as

System.out.println(getTheMinList(List.of(list1, list2)).size());

edited Nov 20 '18 at 17:08

answered Nov 20 '18 at 17:03

nullpointer

46.5k1199191

1

Another suggestion: Try programming to an interface.

– nullpointer
Nov 20 '18 at 17:09

Thank you, i use the var arg because i call the getTheMinList many times with different size arguments.

– zak zak
Nov 20 '18 at 17:40

@zakzak List<List<Integer>> can as well accept varying size outer List as an argument if you'd noticed. This means you can call it as getTheMinList(List.of(List.of(0, 2, 3), List.of(0, 2, 3, 4))) and getTheMinList(List.of(List.of(0, 2, 3), List.of(0, 2, 3, 4), List.of(1,2,3))) as well.

– nullpointer
Nov 20 '18 at 17:42

yes but i should send a list of list as argument every time, in my program i send many list as argument, like getTheMinList(l1,l2) ,getTheMinList(l1,l2,l3) ans so on...and i m using only java 8.

– zak zak
Nov 20 '18 at 17:43

1

@zakzak the return type of min is Optional<T> for which you either check for an Optional.empty or can fallback to a default value using Optional.orElse API.

– nullpointer
Nov 20 '18 at 18:11

|
show 2 more comments

You can use Stream.min comparing the List.size:

public static List<Integer> getTheMinList(List<Integer>... lists){

    return Arrays.stream(lists)

            .min(Comparator.comparingInt(List::size))

            .orElse(new ArrayList<>());

}

or possibly better if you could get rid of var-args and unchecked assignment

private static List<Integer> getTheMinList(List<List<Integer>> lists){

    return lists.stream()

            .min(Comparator.comparingInt(List::size))

            .orElse(new ArrayList<>());

}

// invoked as

System.out.println(getTheMinList(List.of(list1, list2)).size());

edited Nov 20 '18 at 17:08

answered Nov 20 '18 at 17:03

nullpointer

46.5k1199191

1

Another suggestion: Try programming to an interface.

– nullpointer
Nov 20 '18 at 17:09

Thank you, i use the var arg because i call the getTheMinList many times with different size arguments.

– zak zak
Nov 20 '18 at 17:40

@zakzak List<List<Integer>> can as well accept varying size outer List as an argument if you'd noticed. This means you can call it as getTheMinList(List.of(List.of(0, 2, 3), List.of(0, 2, 3, 4))) and getTheMinList(List.of(List.of(0, 2, 3), List.of(0, 2, 3, 4), List.of(1,2,3))) as well.

– nullpointer
Nov 20 '18 at 17:42

yes but i should send a list of list as argument every time, in my program i send many list as argument, like getTheMinList(l1,l2) ,getTheMinList(l1,l2,l3) ans so on...and i m using only java 8.

– zak zak
Nov 20 '18 at 17:43

1

@zakzak the return type of min is Optional<T> for which you either check for an Optional.empty or can fallback to a default value using Optional.orElse API.

– nullpointer
Nov 20 '18 at 18:11

|
show 2 more comments

You can use Stream.min comparing the List.size:

public static List<Integer> getTheMinList(List<Integer>... lists){

    return Arrays.stream(lists)

            .min(Comparator.comparingInt(List::size))

            .orElse(new ArrayList<>());

}

or possibly better if you could get rid of var-args and unchecked assignment

private static List<Integer> getTheMinList(List<List<Integer>> lists){

    return lists.stream()

            .min(Comparator.comparingInt(List::size))

            .orElse(new ArrayList<>());

}

// invoked as

System.out.println(getTheMinList(List.of(list1, list2)).size());

edited Nov 20 '18 at 17:08

answered Nov 20 '18 at 17:03

nullpointer

46.5k1199191

You can use Stream.min comparing the List.size:

public static List<Integer> getTheMinList(List<Integer>... lists){

    return Arrays.stream(lists)

            .min(Comparator.comparingInt(List::size))

            .orElse(new ArrayList<>());

}

or possibly better if you could get rid of var-args and unchecked assignment

private static List<Integer> getTheMinList(List<List<Integer>> lists){

    return lists.stream()

            .min(Comparator.comparingInt(List::size))

            .orElse(new ArrayList<>());

}

// invoked as

System.out.println(getTheMinList(List.of(list1, list2)).size());

edited Nov 20 '18 at 17:08

answered Nov 20 '18 at 17:03

nullpointer

46.5k1199191

edited Nov 20 '18 at 17:08

answered Nov 20 '18 at 17:03

nullpointer

46.5k1199191

answered Nov 20 '18 at 17:03

nullpointer

46.5k1199191

answered Nov 20 '18 at 17:03

nullpointer

46.5k1199191

1

Another suggestion: Try programming to an interface.

– nullpointer
Nov 20 '18 at 17:09

Thank you, i use the var arg because i call the getTheMinList many times with different size arguments.

– zak zak
Nov 20 '18 at 17:40

@zakzak List<List<Integer>> can as well accept varying size outer List as an argument if you'd noticed. This means you can call it as getTheMinList(List.of(List.of(0, 2, 3), List.of(0, 2, 3, 4))) and getTheMinList(List.of(List.of(0, 2, 3), List.of(0, 2, 3, 4), List.of(1,2,3))) as well.

– nullpointer
Nov 20 '18 at 17:42

yes but i should send a list of list as argument every time, in my program i send many list as argument, like getTheMinList(l1,l2) ,getTheMinList(l1,l2,l3) ans so on...and i m using only java 8.

– zak zak
Nov 20 '18 at 17:43

1

@zakzak the return type of min is Optional<T> for which you either check for an Optional.empty or can fallback to a default value using Optional.orElse API.

– nullpointer
Nov 20 '18 at 18:11

|
show 2 more comments

1

Another suggestion: Try programming to an interface.

– nullpointer
Nov 20 '18 at 17:09

Thank you, i use the var arg because i call the getTheMinList many times with different size arguments.

– zak zak
Nov 20 '18 at 17:40

@zakzak List<List<Integer>> can as well accept varying size outer List as an argument if you'd noticed. This means you can call it as getTheMinList(List.of(List.of(0, 2, 3), List.of(0, 2, 3, 4))) and getTheMinList(List.of(List.of(0, 2, 3), List.of(0, 2, 3, 4), List.of(1,2,3))) as well.

– nullpointer
Nov 20 '18 at 17:42

yes but i should send a list of list as argument every time, in my program i send many list as argument, like getTheMinList(l1,l2) ,getTheMinList(l1,l2,l3) ans so on...and i m using only java 8.

– zak zak
Nov 20 '18 at 17:43

1

@zakzak the return type of min is Optional<T> for which you either check for an Optional.empty or can fallback to a default value using Optional.orElse API.

– nullpointer
Nov 20 '18 at 18:11

Another suggestion: Try programming to an interface.

– nullpointer
Nov 20 '18 at 17:09

Thank you, i use the var arg because i call the getTheMinList many times with different size arguments.

– zak zak
Nov 20 '18 at 17:40

@zakzak List<List<Integer>> can as well accept varying size outer List as an argument if you'd noticed. This means you can call it as getTheMinList(List.of(List.of(0, 2, 3), List.of(0, 2, 3, 4))) and getTheMinList(List.of(List.of(0, 2, 3), List.of(0, 2, 3, 4), List.of(1,2,3))) as well.

– nullpointer
Nov 20 '18 at 17:42

yes but i should send a list of list as argument every time, in my program i send many list as argument, like getTheMinList(l1,l2) ,getTheMinList(l1,l2,l3) ans so on...and i m using only java 8.

– zak zak
Nov 20 '18 at 17:43

@zakzak the return type of min is Optional<T> for which you either check for an Optional.empty or can fallback to a default value using Optional.orElse API.

– nullpointer
Nov 20 '18 at 18:11

|
show 2 more comments

Just another idea...

as @NullPointer suggested, I’d make the method take a List<List<Integer>> rather than the varargs.

Given this change you can simply do:

Collections.min(lists, Comparator.comparingInt(List::size));

Short, simple and readable right?

answered Nov 20 '18 at 17:22

Aomine

41.9k74071

thank you, i will review my code.in general every list should be not null before the call.

– zak zak
Nov 20 '18 at 17:47

1

When you stay with varargs, you can still use this solution as simple as return Collections.min(Arrays.asList(lists), Comparator.comparingInt(List::size)); This uses Arrays.asList which creates a lightweight wrapper around the array, allowing to apply the entirety of the Collection API on an existing array…

– Holger
Nov 21 '18 at 8:54

add a comment |

Just another idea...

as @NullPointer suggested, I’d make the method take a List<List<Integer>> rather than the varargs.

Given this change you can simply do:

Collections.min(lists, Comparator.comparingInt(List::size));

Short, simple and readable right?

answered Nov 20 '18 at 17:22

Aomine

41.9k74071

thank you, i will review my code.in general every list should be not null before the call.

– zak zak
Nov 20 '18 at 17:47

1

When you stay with varargs, you can still use this solution as simple as return Collections.min(Arrays.asList(lists), Comparator.comparingInt(List::size)); This uses Arrays.asList which creates a lightweight wrapper around the array, allowing to apply the entirety of the Collection API on an existing array…

– Holger
Nov 21 '18 at 8:54

add a comment |

Just another idea...

as @NullPointer suggested, I’d make the method take a List<List<Integer>> rather than the varargs.

Given this change you can simply do:

Collections.min(lists, Comparator.comparingInt(List::size));

Short, simple and readable right?

answered Nov 20 '18 at 17:22

Aomine

41.9k74071

Just another idea...

as @NullPointer suggested, I’d make the method take a List<List<Integer>> rather than the varargs.

Given this change you can simply do:

Collections.min(lists, Comparator.comparingInt(List::size));

Short, simple and readable right?

answered Nov 20 '18 at 17:22

Aomine

41.9k74071

answered Nov 20 '18 at 17:22

Aomine

41.9k74071

answered Nov 20 '18 at 17:22

Aomine

41.9k74071

answered Nov 20 '18 at 17:22

Aomine

41.9k74071

thank you, i will review my code.in general every list should be not null before the call.

– zak zak
Nov 20 '18 at 17:47

1

When you stay with varargs, you can still use this solution as simple as return Collections.min(Arrays.asList(lists), Comparator.comparingInt(List::size)); This uses Arrays.asList which creates a lightweight wrapper around the array, allowing to apply the entirety of the Collection API on an existing array…

– Holger
Nov 21 '18 at 8:54

add a comment |

thank you, i will review my code.in general every list should be not null before the call.

– zak zak
Nov 20 '18 at 17:47

1

When you stay with varargs, you can still use this solution as simple as return Collections.min(Arrays.asList(lists), Comparator.comparingInt(List::size)); This uses Arrays.asList which creates a lightweight wrapper around the array, allowing to apply the entirety of the Collection API on an existing array…

– Holger
Nov 21 '18 at 8:54

thank you, i will review my code.in general every list should be not null before the call.

– zak zak
Nov 20 '18 at 17:47

When you stay with varargs, you can still use this solution as simple as return Collections.min(Arrays.asList(lists), Comparator.comparingInt(List::size)); This uses Arrays.asList which creates a lightweight wrapper around the array, allowing to apply the entirety of the Collection API on an existing array…

– Holger
Nov 21 '18 at 8:54

add a comment |

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