如何创建频率表（整数数组）

Question

I made an int[] array that will be fill by score from users input. My task is to create a frequency table, which count how many times did a certain score entered by the user. Example: user entered the following score, 13,13,13,16,16,19,22. Then, in a tabular form 13 - 3 ,16 - 2, 19 - 1, 22 - 1. Sorry bad english

Answer 1

You can do something like:

Map<Integer, Integer> numberCountMap = ....
for (int i=0; i<numbers.length; i++) {
     numberCountMap.compute(numbers[i], (key, value) -> value == null ? 1 : value + 1);
}   
//print map or sort by value if you need most frequent one to be on top

Answer 2

This will do the job

import java.util.HashSet;
import java.util.Set;
public class NumbersInArray {
    public static void main(String[] args) {
        int [] arr = {1,2,1,1,5,5,5,3,4,5,6};
        Set<Integer> set = new HashSet();

        //adding numbers to set will remove duplicates
        for(int i =0 ; i<arr.length;i++) {
            set.add(arr[i]);
        }
        int counter = 0;
        int[] arrayToCheck = set.stream().mapToInt(Number::intValue).toArray();
        for(int i = 0; i<set.size(); i++) {
            counter = 0;
            for(int j =0; j<arr.length;j++) {
                if(arrayToCheck[i]== arr[j]) {
                    counter++;
                }   
            }
            System.out.println(arrayToCheck[i] + "-" + counter);
        }
    }
}

Answer 3

In Java 8 you can do this

Map<Integer, Long> freq = Arrays.stream(array).boxed().
                collect(Collectors.groupingBy(Integer::intValue, Collectors.counting()));