| /* ==================================================================== |
| 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. |
| ==================================================================== */ |
| |
| package org.apache.poi.ss.formula.functions; |
| |
| import java.util.Arrays; |
| |
| /** |
| * @author Amol S. Deshmukh < amolweb at ya hoo dot com > |
| * |
| * Library for common statistics functions |
| */ |
| final class StatsLib { |
| |
| private StatsLib() { |
| // no instances of this class |
| } |
| |
| |
| /** |
| * 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 var(double[] v) { |
| double r = Double.NaN; |
| if (v!=null && v.length > 1) { |
| r = devsq(v) / (v.length - 1); |
| } |
| return r; |
| } |
| |
| public static double varp(double[] v) { |
| double r = Double.NaN; |
| if (v!=null && v.length > 1) { |
| r = devsq(v) /v.length; |
| } |
| 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 |
| */ |
| public static double kthLargest(double[] v, int k) { |
| double r = Double.NaN; |
| int index = k-1; // since arrays are 0-based |
| if (v!=null && v.length > index && index >= 0) { |
| Arrays.sort(v); |
| r = v[v.length-index-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; |
| int index = k-1; // since arrays are 0-based |
| if (v!=null && v.length > index && index >= 0) { |
| Arrays.sort(v); |
| r = v[index]; |
| } |
| return r; |
| } |
| } |