tabulate.js (2260B)
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 isCollection = require( '@stdlib/assert/is-collection' ); 24 var indexOf = require( './../../index-of' ); 25 26 27 // MAIN // 28 29 /** 30 * Generates a frequency table. 31 * 32 * ## Notes 33 * 34 * - The output is an array of arrays. Each sub-array corresponds to a unique value in the input collection and is structured as follows: 35 * 36 * - 0: unique value 37 * - 1: value count 38 * - 2: frequency percentage 39 * 40 * 41 * @param {Collection} collection - input collection 42 * @throws {TypeError} first argument must be a collection 43 * @returns {(Array<Array>|Array)} frequency table 44 * 45 * @example 46 * var arr = [ 'beep', 'boop', 'foo', 'beep' ]; 47 * 48 * var out = tabulate( arr ); 49 * // returns [ [ 'beep', 2, 0.5 ], [ 'boop', 1, 0.25 ], [ 'foo', 1, 0.25 ] ] 50 */ 51 function tabulate( collection ) { 52 var count; 53 var tmp; 54 var len; 55 var out; 56 var v; 57 var i; 58 var j; 59 if ( !isCollection( collection ) ) { 60 throw new TypeError( 'invalid argument. First argument must be a collection. Value: `'+collection+'`.' ); 61 } 62 count = 0; 63 tmp = []; 64 out = []; 65 66 // For each collection element, determine if we've seen the element before. If not, cache a reference which points to its location in the output array; otherwise, update the running count. 67 len = collection.length; 68 for ( i = 0; i < len; i++ ) { 69 v = collection[ i ]; 70 count += 1; 71 j = indexOf( tmp, v ); 72 if ( j === -1 ) { 73 tmp.push( v ); 74 out.push( [ v, 1, 0 ] ); 75 } else { 76 out[ j ][ 1 ] += 1; 77 } 78 } 79 // Compute percentages... 80 len = out.length; 81 for ( i = 0; i < len; i++ ) { 82 out[ i ][ 2 ] = out[ i ][ 1 ] / count; 83 } 84 return out; 85 } 86 87 88 // EXPORTS // 89 90 module.exports = tabulate;