如何获取大小为X的Java集并进入X / Y集？

I have a Java Set (specifically HashSet). Suppose it has a size of 10k. How can I break it into 5 Sets each of size 2k?

我有一个Java Set（特别是HashSet）。假设它的大小为10k。如何将其分为5套每个尺寸2k？

5 个解决方案

#1

This method will split the elements of the set so that the first set contains the first 2000, the second contains the next 2000, etc.

此方法将拆分集合的元素，以便第一个集合包含第一个2000，第二个集合包含下一个2000，等等。

public static <T> List<Set<T>> split(Set<T> original, int count) {
    // Create a list of sets to return.
    ArrayList<Set<T>> result = new ArrayList<Set<T>>(count);

    // Create an iterator for the original set.
    Iterator<T> it = original.iterator();

    // Calculate the required number of elements for each set.
    int each = original.size() / count;

    // Create each new set.
    for (int i = 0; i < count; i++) {
        HashSet<T> s = new HashSet<T>(original.size() / count + 1);
        result.add(s);
        for (int j = 0; j < each && it.hasNext(); j++) {
            s.add(it.next());
        }
    }
    return result;
}

//As example, in your code...

Set<Integer> originalSet = new HashSet<Integer>();
// [fill the set...]
List<Set<Integer>> splitSets = split(originalSet, 5);
Set<Integer> first = splitSets.get(0); // etc.

#2

Guava has libraries to partition Iterable classes. The Iterables is a utility class which has static methods to partition Iterable classes. The return value is a Iterable of lists though. The given code shows how to do that.

Guava有用于分区Iterable类的库。 Iterables是一个实用程序类，它具有分区Iterable类的静态方法。返回值虽然是Iterable列表。给定的代码显示了如何执行此操作。

Set<Integer> myIntSet = new HashSet<Integer>();
// fill the set
Iterable<List<Integer>> lists = Iterables.partition(myIntSet, SIZE_EACH_PARTITION);

#3

Iterate over the entire set, and add the first 2000 elements to a first new set, the 2nd 2000 elements to the 2nd new set, etc.

迭代整个集合，将前2000个元素添加到第一个新集合，将第二个2000个元素添加到第二个新集合等。

#4

If you do not want to write it by your own have a look at guava. The Lists class have a method partition(List, int) to split a list into multiple lists with the specified size. See Guava Lists

如果你不想自己写它看看番石榴。 Lists类有一个方法分区（List，int），用于将列表拆分为具有指定大小的多个列表。参见番石榴名单

#5

I've written something that does the splitting of the set.

我写了一些东西，分裂了集合。

It uses intermediate arrays and Lists.

它使用中间数组和列表。

It uses the Arrays.asList and the Arrays.copyOfRange methods.

它使用Arrays.asList和Arrays.copyOfRange方法。

import java.util.Arrays;
import java.util.HashSet;
import java.util.Set;


public class SetSplitTest {
    //define and initialize set
    private static Set<Integer> largeSet;
    static {
        largeSet  = new HashSet<Integer>();

        for (int i = 0; i < 10000; i++) {
            largeSet.add(i);
        }
    }


    public static void main() {
        System.out.println(largeSet);
        int amountOfSets = 5; //amount of subsets wanted
        Set<Integer>[] subsets = new Set[amountOfSets]; //array holding the subsets

        Integer[] largesetarray =  largeSet.toArray(new Integer[largeSet.size()]);

        for (int i = 1; i <= amountOfSets; i++) {
            int fromIndex = (i-1) * largeSet.size() / amountOfSets;
            int toIndex = i * largeSet.size() / amountOfSets - 1; 
            Set<Integer> subHashSet = new HashSet<Integer>();
            subHashSet.addAll(Arrays.asList(Arrays.copyOfRange(largesetarray, fromIndex, toIndex)));

            subsets[i - 1] = subHashSet;
        }

        for (Set<Integer> subset : subsets) {
            System.out.println(subset);
        }
    }
}

This definately not the most elegant solution, but it's the best i could think off at the moment when not wanting to loop the sets yourself.

这绝对不是最优雅的解决方案，但它是我不能想要自己循环设置的那一刻想到的最好的。

#1