median.js (1680B)
1 /** 2 * @license Apache-2.0 3 * 4 * Copyright (c) 2018 The Stdlib Authors. 5 * 6 * Licensed under the Apache License, Version 2.0 (the "License"); 7 * you may not use this file except in compliance with the License. 8 * You may obtain a copy of the License at 9 * 10 * http://www.apache.org/licenses/LICENSE-2.0 11 * 12 * Unless required by applicable law or agreed to in writing, software 13 * distributed under the License is distributed on an "AS IS" BASIS, 14 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 15 * See the License for the specific language governing permissions and 16 * limitations under the License. 17 */ 18 19 'use strict'; 20 21 // MODULES // 22 23 var floor = require( '@stdlib/math/base/special/floor' ); 24 25 26 // FUNCTIONS // 27 28 /** 29 * Comparator function used to sort values in ascending order. 30 * 31 * @private 32 * @param {number} a - first number 33 * @param {number} b - second number 34 * @returns {number} difference between `a` and `b` 35 */ 36 function ascending( a, b ) { 37 return a - b; 38 } 39 40 41 // MAIN // 42 43 /** 44 * Computes the median of an array. 45 * 46 * @param {Array} arr - input array 47 * @returns {number} median value 48 */ 49 function median( arr ) { 50 var len = arr.length; 51 var id; 52 var d; 53 var i; 54 55 if ( !len ) { 56 return null; 57 } 58 59 // Copy and sort data in ascending order: 60 d = []; 61 for ( i = 0; i < len; i++ ) { 62 d.push( arr[ i ] ); 63 } 64 d.sort( ascending ); 65 66 // Get the middle index: 67 id = floor( len / 2 ); 68 69 if ( len % 2 ) { 70 // The number of elements is not evenly divisible by two, hence we have a middle index: 71 return d[ id ]; 72 } 73 // Even number of elements, so must take the mean of the two middle values: 74 return ( d[ id-1 ] + d[ id ] ) / 2.0; 75 } 76 77 78 // EXPORTS // 79 80 module.exports = median;