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  1. /* package whatever; // don't place package name! */
  2.  
  3. import java.util.*;
  4. import java.lang.*;
  5. import java.io.*;
  6. import java.util.ArrayList;
  7. import java.util.List;
  8. import java.util.Map;
  9. import java.util.function.Predicate;
  10. import java.util.stream.Collectors;
  11.  
  12. /* Name of the class has to be "Main" only if the class is public. */
  13. class Ideone
  14. {
  15. 	public static void main (String[] args) throws java.lang.Exception
  16. 	{
  17. 		//My silly test predicate
  18. 		Predicate<String> p = s -> s.length() > 4;
  19.  
  20. 		//List with test strings (even though it's called numbers...)
  21.         List<String> numbers = new ArrayList<>(List.of("Ted", "James", "Bobby", "Mark", "Hank", "Richard"));
  22.  
  23. 		//Partitioning by your first example
  24.         Map<Boolean, List<String>> partitioned = numbers.stream()
  25.                 .collect(Collectors.partitioningBy(p));
  26.  
  27. 		//Printing the result
  28.         System.out.println(partitioned);
  29.  
  30. 		//Partitioning with int keys
  31.         Map<Integer, List<String>> partitioned2 = numbers.stream()
  32.                 .collect(Collectors.toMap(s -> p.test(s) ? 1 : 0, s -> new ArrayList<>(List.of(s)), (list1, list2) -> {
  33.                     list1.addAll(list2);
  34.                     return list1;
  35.                 }));
  36.  
  37. 		//Printing the second partition to compare it with the first one
  38.         System.out.println(partitioned2);
  39. 	}
  40. }
Success #stdin #stdout 0.12s 52448KB
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{false=[Ted, Mark, Hank], true=[James, Bobby, Richard]}
{0=[Ted, Mark, Hank], 1=[James, Bobby, Richard]}
https://ideone.com/Kd8xrI
Java 8 Stream change key during partitioning

https://stackoverflow.com/questions/72223947/java-8-stream-change-key-during-partitioning/
language:
Java (HotSpot 12)
created:
2 years ago
visibility:
public

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