statslib.java

来自「EXCEL read and write」· Java 代码 · 共 141 行

/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements.  See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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.
*/
/*
 * Created on May 30, 2005
 *
 */
package org.apache.poi.hssf.record.formula.functions;

import java.util.Arrays;

/**
 * @author Amol S. Deshmukh < amolweb at ya hoo dot com >
 *
 * Library for common statistics functions
 */
public final class StatsLib {

    private StatsLib() {}


    /**
     * returns the mean of deviations from mean.
     * @param v
     */
    public static double avedev(double[] v) {
        double r = 0;
        double m = 0;
        double s = 0;
        for (int i=0, iSize=v.length; i<iSize; i++) {
            s += v[i];
        }
        m = s / v.length;
        s = 0;
        for (int i=0, iSize=v.length; i<iSize; i++) {
            s += Math.abs(v[i]-m);
        }
        r = s / v.length;
        return r;
    }
    
    public static double stdev(double[] v) {
        double r = Double.NaN;
        if (v!=null && v.length > 1) {
            r = Math.sqrt( devsq(v) / (v.length - 1) );
        }
        return r;
    }
    
    
    public static double median(double[] v) {
        double r = Double.NaN;
        
        if (v!=null && v.length >= 1) {
            int n = v.length;
            Arrays.sort(v);
            r = (n % 2 == 0)
                ? (v[n / 2] + v[n / 2 - 1]) / 2
                : v[n / 2];
        }
        
        return r;
    }
    
    
    public static double devsq(double[] v) {
        double r = Double.NaN;
        if (v!=null && v.length >= 1) {
            double m = 0;
            double s = 0;
            int n = v.length;
            for (int i=0; i<n; i++) {
                s += v[i];
            }
            m = s / n;
            s = 0;
            for (int i=0; i<n; i++) {
                s += (v[i]- m) * (v[i] - m);
            }
            
            r = (n == 1)
                    ? 0
                    : s;
        }
        return r;
    }
    
    /**
     * returns the kth largest element in the array. Duplicates
     * are considered as distinct values. Hence, eg.
     * for array {1,2,4,3,3} & k=2, returned value is 3.
     * <br/>
     * k <= 0 & k >= v.length and null or empty arrays
     * will result in return value Double.NaN
     * @param v
     * @param k
     */
    public static double kthLargest(double[] v, int k) {
        double r = Double.NaN;
        k--; // since arrays are 0-based
        if (v!=null && v.length > k && k >= 0) {
            Arrays.sort(v);
            r = v[v.length-k-1];
        }
        return r;
    }

    /**
     * returns the kth smallest element in the array. Duplicates
     * are considered as distinct values. Hence, eg.
     * for array {1,1,2,4,3,3} & k=2, returned value is 1.
     * <br/>
     * k <= 0 & k >= v.length or null array or empty array
     * will result in return value Double.NaN
     * @param v
     * @param k
     */
    public static double kthSmallest(double[] v, int k) {
        double r = Double.NaN;
        k--; // since arrays are 0-based
        if (v!=null && v.length > k && k >= 0) {
            Arrays.sort(v);
            r = v[k];
        }
        return r;
    }
}