com.opengamma.analytics.math.statistics.descriptive.ModeCalculator.java Source code

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Here is the source code for com.opengamma.analytics.math.statistics.descriptive.ModeCalculator.java

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/**
 * Copyright (C) 2009 - present by OpenGamma Inc. and the OpenGamma group of companies
 * 
 * Please see distribution for license.
 */
package com.opengamma.analytics.math.statistics.descriptive;

import java.util.Arrays;
import java.util.TreeMap;

import org.apache.commons.lang.Validate;

import com.opengamma.analytics.math.MathException;
import com.opengamma.analytics.math.function.Function1D;

/**
 * The mode of a series of data is the value that occurs more frequently in the data set.
 */
public class ModeCalculator extends Function1D<double[], Double> {
    private static final double EPS = 1e-16;

    //TODO more than one value can be the mode
    /**
     * @param x The array of data, not null or empty
     * @return The arithmetic mean
     */
    @Override
    public Double evaluate(final double[] x) {
        Validate.notNull(x, "x");
        Validate.isTrue(x.length > 0, "x cannot be empty");
        if (x.length == 1) {
            return x[0];
        }
        final double[] x1 = Arrays.copyOf(x, x.length);
        Arrays.sort(x1);
        final TreeMap<Integer, Double> counts = new TreeMap<Integer, Double>();
        int count = 1;
        for (int i = 1; i < x1.length; i++) {
            if (Math.abs(x1[i] - x1[i - 1]) < EPS) {
                count++;
            } else {
                counts.put(count, x1[i - 1]);
                count = 1;
            }
        }
        if (counts.lastKey() == 1) {
            throw new MathException("Could not find mode for array; no repeated values");
        }
        return counts.lastEntry().getValue();
    }
}