Java stddev stdDev(T[] array)

Description

Returns the population standard deviation of the given values.

License

Apache License

Parameter

Parameter	Description
array	input values
T	number type

Return

the population standard deviation

Declaration

public static <T extends Number> double stdDev(T[] array) 

Method Source Code

//package com.java2s;
/**//w w  w  .  j  av a  2 s.com
 * Copyright 2014 SAP AG
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.util.Collection;

public class Main {
    /**
     * Returns the population standard deviation of the given values.
     * 
     * @param values
     *            input values
     * @return the population standard deviation
     */
    public static double stdDev(double[] values) {
        double result = 0;

        if (values == null) {
            throw new IllegalArgumentException(
                    "Cannot calculate standard deviation on a null object.");
        }

        if (values.length < 1) {
            throw new IllegalArgumentException(
                    "Cannot calculated standard deviation on an empty set.");
        }

        final double mean = average(values);

        for (double v : values) {
            result += (v - mean) * (v - mean);
        }

        result = Math.sqrt(result / values.length);

        return result;
    }

    /**
     * Returns the population standard deviation of the given values.
     * 
     * @param array
     *            input values
     * @param <T>
     *            number type
     * @return the population standard deviation
     * 
     */
    public static <T extends Number> double stdDev(T[] array) {
        double[] temp = new double[array.length];
        for (int i = 0; i < array.length; i++) {
            temp[i] = array[i].doubleValue();
        }
        return stdDev(temp);
    }

    /**
     * Returns the population standard deviation of the given values.
     * 
     * @param values
     *            input values
     * @param <T>
     *            number type
     * @return the population standard deviation
     */
    public static <T extends Number> double stdDev(Collection<T> values) {
        return stdDev(values.toArray(new Number[] {}));
    }

    /**
     * Returns the average (mean) of the given values.
     * 
     * @param values
     *            a collection of values
     * @return the average as a double value
     */
    public static double average(Collection<? extends Number> values) {
        double result = 0;

        if (values == null) {
            throw new IllegalArgumentException(
                    "Cannot calculate average on a null object.");
        }

        if (values.size() == 0) {
            return 0;
        } else {
            for (Number n : values) {
                result += n.doubleValue();
            }
        }

        return result / values.size();
    }

    /**
     * Returns the average (mean) of the given values.
     * 
     * @param values
     *            an array of values
     * @return the average as a double value
     */
    public static double average(double[] values) {
        double result = 0;

        if (values == null) {
            throw new IllegalArgumentException(
                    "Cannot calculate average on a null object.");
        }

        if (values.length == 0) {
            return 0;
        } else {
            for (Number n : values) {
                result += n.doubleValue();
            }
        }

        return result / values.length;

    }
}

Related

1. stddev(float[] data)
2. stddev(int[] values, int start, int length)
3. stdDev(Integer[] values)
4. stddev(long[] samples)
5. stddev(Number[] array, boolean isSample)
6. stdDeviation(int[] data)
7. stdev(Collection values)
8. stdev(Collection values)
9. stdev(double... array)