java clump list

To "clump" a list in Java, you can use the groupingBy method of the Collectors class to create a map of lists, grouping the elements of the list by a certain criteria.

Here's an example of how to "clump" a list of integers into groups of even and odd numbers:

import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;

public class Main {
  public static void main(String[] args) {
    List<Integer> numbers = List.of(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);

    Map<Boolean, List<Integer>> clumped = numbers.stream()
        .collect(Collectors.groupingBy(n -> n % 2 == 0));

    System.out.println(clumped);  // Outputs: {false=[1, 3, 5, 7, 9], true=[2, 4, 6, 8, 10]}
  }
}

In this example, the groupingBy method is used to create a map of lists, grouping the elements of the numbers list by their parity (even or odd). The resulting map has two keys, true and false, corresponding to the even and odd numbers, respectively.

You can use a similar approach to "clump" a list by any other criteria. For example, to "clump" a list of strings by their length:

List<String> words = List.of("apple", "banana", "cherry", "date", "elderberry", "fig");

Map<Integer, List<String>> clumped = words.stream()
    .collect(Collectors.groupingBy(String::length));

System.out.println(clumped);  // Outputs: {5=[apple], 6=[banana], 6=[cherry], 4=[date], 10=[elderberry], 3=[fig]}

In this example, the groupingBy method is used to create a map of lists, grouping the elements of the words list by their length. The resulting map has keys representing the different lengths of the strings, and values containing the strings of that length.

Keep in mind that the groupingBy method returns a Collector, which is an intermediate object that can be used to perform further operations on the result of the grouping. You can use the Collectors class to perform various operations on the collector, such as reducing the elements to a single value, or transforming the elements in some way.