Relative frequency in java

问题

I want to create a program to help me with the statistics, but I'm having problems from the beginning and I'm making a huge mess to calculate the relative frequency of an array with random numbers and only one dimension.

For example to generate these numbers:

{3, 5, 5, 2, 4, 1, 3, 5, 4}

I want that the program tell me that the 3 is repeated 2 times, the 4 3 times and 5 5 times

I've created a class to sort these values in order to calculate the median, the first and third quartile, but I still do not know how to find the frequency in order to calculate other values

Thanks for your time

PS: Do not know if this affects anything but I'm using netbeans

回答1:

You are looking for this for sure: Collections: frequency

If you dont have a Collection, convert your array to list first:

Collections.frequency(Arrays.asList(yourArray), new Integer(3))

回答2:

If your range of numbers is relatively small, using an array of counters could be preferred. For example, if your random numbers are in the interval [1,5] then you can use an array of size 5 to store and update the frequency counters:

int[] numbers = {3, 5, 5, 2, 4, 1, 3, 5, 4} ;
int[] frequencies = new int[5];

for(int n : numbers)
    frequencies[n-1]++;

Output array (frequencies):

1 1 2 2 3

EDIT:

This method can be applied to all ranges. For example, let's say you have numbers in the range [500,505]:

int[] frequencies = new int[6];

for(int n : numbers)
    frequencies[n-500]++;

回答3:

Edit: You can use a map for storing frequency like below :

import java.util.HashMap;
import java.util.Map;

public class Frequency {
    public static void main(String[] args) {
        int[] nums = { 3, 5, 5, 2, 4, 1, 3, 5, 4 };
        int count = 1;
        // number,frequency type map.
        Map<Integer, Integer> frequencyMap = new HashMap<Integer, Integer>();
        for (int i = 0; i < nums.length; i++) {
            if (nums[i] != -1) {
                for (int j = i + 1; j < nums.length; j++) {
                    if (nums[j] != -1) {
                        if (nums[i] == nums[j]) {
                            // -1 is an indicator that this number is already counted.
                            // You should replace it such a number which is sure to be not coming in array.
                            nums[j] = -1;
                            count++;
                        }
                    }
                }
                frequencyMap.put(nums[i], count);
                count = 1;
            }
        }
        for (Map.Entry<Integer, Integer> entry : frequencyMap.entrySet()) {
            System.out.println(" Number :" + entry.getKey()
                    + " has frequence :" + entry.getValue());
        }
    }
}

With Output :

 Number :1 has frequence :1
 Number :2 has frequence :1
 Number :3 has frequence :2
 Number :4 has frequence :2
 Number :5 has frequence :3

回答4:

    int[] numbers = {100, 101, 102, 103, 5 , 4, 4 , 6} ;

    Map<Integer, Integer> m = new HashMap<Integer, Integer>();
    for(int num: numbers){
        if(m.containsKey(num)){
            m.put(num, m.get(num)+1);
        }else{
            m.put(num, 1);
        }   
    }
    for (Map.Entry<Integer, Integer> entry : m.entrySet()) {
        System.out.println("Key: " + entry.getKey() + " | Frequencey: " + entry.getValue());
    }

来源：https://stackoverflow.com/questions/14266989/relative-frequency-in-java

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frequency