Print unique values from collection using Stream API [duplicate]

问题

I need to get only unique values from the collection( values which do not have any dublicates in collection). For example, this code:

ArrayList<Integer> g =  new ArrayList<>(Arrays.asList(1,1,2,2,3,4,5,5,5,6,6));
System.out.println(Arrays.toString(g.stream().mapToInt(Integer::intValue).distinct().toArray()));

gives me this result:

[1, 2, 3, 4, 5, 6]

However I want the result:

[3, 4]

Is there any way to do it with Stream API?

回答1:

List<Integer> source = Arrays.asList(1, 1, 2, 2, 3, 4, 5, 5, 5, 6, 6);
List<Integer> processed = source.stream()
        .collect(Collectors.groupingBy(Function.identity(), Collectors.counting()))
        .entrySet().stream()
        .filter(e -> e.getValue() == 1)
        .map(Map.Entry::getKey)
        .collect(Collectors.toList());
System.out.println(processed);

Result:

[3, 4]

回答2:

You can do it as follows:

import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import java.util.stream.Collectors;

public class Collusion {

    public static void main(String[] args) {
        List<Integer> g = Arrays.asList(1, 1, 2, 2, 3, 4, 5, 5, 5, 6, 6);
        System.out.println(g.stream().filter(x -> Collections.frequency(g, x) < 2).collect(Collectors.toList()));
    }
}

Output:

[3, 4]

来源：https://stackoverflow.com/questions/60605971/print-unique-values-from-collection-using-stream-api

标签

java

java-stream