factory.js (4780B)
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 isFunction = require( '@stdlib/assert/is-function' ); 24 var isCollection = require( '@stdlib/assert/is-collection' ); 25 var PINF = require( '@stdlib/constants/float64/pinf' ); 26 var validate = require( './validate.js' ); 27 var limit = require( './limit.js' ); 28 29 30 // MAIN // 31 32 /** 33 * Returns a function for generating a frequency table according to an indicator function. 34 * 35 * ## Notes 36 * 37 * - This function does **not** guarantee that execution is asynchronous. To do so, wrap the `done` callback in a function which either executes at the end of the current stack (e.g., `nextTick`) or during a subsequent turn of the event loop (e.g., `setImmediate`, `setTimeout`). 38 * 39 * - The output frequency table is an array of arrays. Each sub-array corresponds to a unique value in the input collection and is structured as follows: 40 * 41 * - 0: unique value 42 * - 1: value count 43 * - 2: frequency percentage 44 * 45 * 46 * @param {Options} [options] - function options 47 * @param {*} [options.thisArg] - execution context 48 * @param {PositiveInteger} [options.limit] - maximum number of pending invocations at any one time 49 * @param {boolean} [options.series=false] - boolean indicating whether to wait for a previous invocation to complete before invoking a provided function for the next element in a collection 50 * @param {Function} indicator - function whose return values are used to populate the output frequency table 51 * @throws {TypeError} options argument must be an object 52 * @throws {TypeError} must provide valid options 53 * @throws {TypeError} last argument must be a function 54 * @returns {Function} function which invokes the indicator function once for each element in a collection 55 * 56 * @example 57 * var readFile = require( '@stdlib/fs/read-file' ); 58 * 59 * function indicator( file, next ) { 60 * var opts = { 61 * 'encoding': 'utf8' 62 * }; 63 * readFile( file, opts, onFile ); 64 * 65 * function onFile( error ) { 66 * if ( error ) { 67 * return next( null, 'nonreadable' ); 68 * } 69 * next( null, 'readable' ); 70 * } 71 * } 72 * 73 * var opts = { 74 * 'series': true 75 * }; 76 * 77 * // Create a `tabulateByAsync` function which invokes the indicator function for each collection element sequentially: 78 * var tabulateByAsync = factory( opts, indicator ); 79 * 80 * // Create a collection over which to iterate: 81 * var files = [ 82 * './beep.js', 83 * './boop.js' 84 * ]; 85 * 86 * // Define a callback which handles results: 87 * function done( error, result ) { 88 * if ( error ) { 89 * throw error; 90 * } 91 * console.log( result ); 92 * } 93 * 94 * // Try to read each element in `files`: 95 * tabulateByAsync( files, done ); 96 */ 97 function factory( options, indicator ) { 98 var opts; 99 var err; 100 var f; 101 102 opts = {}; 103 if ( arguments.length > 1 ) { 104 err = validate( opts, options ); 105 if ( err ) { 106 throw err; 107 } 108 f = indicator; 109 } else { 110 f = options; 111 } 112 if ( !isFunction( f ) ) { 113 throw new TypeError( 'invalid argument. Last argument must be a function. Value: `'+f+'`.' ); 114 } 115 if ( opts.series ) { 116 opts.limit = 1; 117 } else if ( !opts.limit ) { 118 opts.limit = PINF; 119 } 120 return tabulateByAsync; 121 122 /** 123 * Invokes an indicator function for each element in a collection. 124 * 125 * @private 126 * @param {Collection} collection - input collection 127 * @param {Callback} done - function to invoke upon completion 128 * @throws {TypeError} first argument must be a collection 129 * @throws {TypeError} last argument must be a function 130 * @returns {void} 131 */ 132 function tabulateByAsync( collection, done ) { 133 if ( !isCollection( collection ) ) { 134 throw new TypeError( 'invalid argument. First argument must be a collection. Value: `'+collection+'.`' ); 135 } 136 if ( !isFunction( done ) ) { 137 throw new TypeError( 'invalid argument. Last argument must be a function. Value: `'+done+'`.' ); 138 } 139 return limit( collection, opts, f, clbk ); 140 141 /** 142 * Callback invoked upon completion. 143 * 144 * @private 145 * @param {*} [error] - error 146 * @param {Object} result - frequency table 147 * @returns {void} 148 */ 149 function clbk( error, result ) { 150 if ( error ) { 151 return done( error ); 152 } 153 done( null, result ); 154 } 155 } 156 } 157 158 159 // EXPORTS // 160 161 module.exports = factory;