Calculates Spearman's rank correlation coefficient - Java Algorithm

Java examples for Algorithm:Statistics

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Description

Calculates Spearman's rank correlation coefficient

Demo Code


import java.util.Scanner;
import java.util.Arrays;
import java.util.Comparator;

/* O(n log n) runtime. O(n) space
 *
 *//* w  w  w  . j  a  v a  2s . co m*/
public class Solution {

    public static void main(String[] args) {
        /* Read and save input */
        Scanner scan = new Scanner(System.in);
        int size = scan.nextInt();
        double [] X = new double[size];
        double [] Y = new double[size];
        for (int i = 0; i < size; i++) {
            X[i] = scan.nextDouble();
        }
        for (int i = 0; i < size; i++) {
            Y[i] = scan.nextDouble();
        }
        
        System.out.format("%.3f", spearman(X, Y));
    }
    
    /* Calculates Spearman's rank correlation coefficient, */
    private static Double spearman(double [] X, double [] Y) {
        /* Error check */
        if (X == null || Y == null || X.length != Y.length) {
            return null;
        }
        
        /* Create Rank arrays */
        int [] rankX = getRanks(X);
        int [] rankY = getRanks(Y);

        /* Apply Spearman's formula */
        int n = X.length;
        double numerator = 0;
        for (int i = 0; i < n; i++) {
            numerator += Math.pow((rankX[i] - rankY[i]), 2);
        }
        numerator *= 6;
        return 1 - numerator / (n * ((n * n) - 1));
    }
    
    /* Returns a new array with ranks. Assumes unique array values. */
    public static int[] getRanks(double [] array) {
        int n = array.length;
        
        /* Create Pair[] and sort by values */
        Pair [] pair = new Pair[n];
        for (int i = 0; i < n; i++) {
            pair[i] = new Pair(i, array[i]);
        }
        Arrays.sort(pair, new PairValueComparator());

        /* Create and return ranks[] */
        int [] ranks = new int[n];
        int rank = 1;
        for (Pair p : pair) {
            ranks[p.index] = rank++;
        }
        return ranks;
    }
    
    /* A class to store 2 variables */
    public static class Pair {
        public final int index;
        public final double value;
 
        public Pair(int i, double v) {
            index = i;
            value = v;
        }
    }

    /* This lets us sort Pairs based on their value field */
    public static class PairValueComparator implements Comparator<Pair> {
        @Override
        public int compare(Pair p1, Pair p2) {
            if (p1.value < p2.value) {
                return -1;
            } else if (p1.value > p2.value) {
                return 1;
            } else {
                return 0;
            }
        }
    }
}

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