README.md (5465B)
1 <!-- 2 3 @license Apache-2.0 4 5 Copyright (c) 2018 The Stdlib Authors. 6 7 Licensed under the Apache License, Version 2.0 (the "License"); 8 you may not use this file except in compliance with the License. 9 You may obtain a copy of the License at 10 11 http://www.apache.org/licenses/LICENSE-2.0 12 13 Unless required by applicable law or agreed to in writing, software 14 distributed under the License is distributed on an "AS IS" BASIS, 15 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 16 See the License for the specific language governing permissions and 17 limitations under the License. 18 19 --> 20 21 # inmapRight 22 23 > Invoke a function for each element in a collection and update the collection in-place, iterating from right to left. 24 25 <!-- Section to include introductory text. Make sure to keep an empty line after the intro `section` element and another before the `/section` close. --> 26 27 <section class="intro"> 28 29 </section> 30 31 <!-- /.intro --> 32 33 <!-- Package usage documentation. --> 34 35 <section class="usage"> 36 37 ## Usage 38 39 ```javascript 40 var inmapRight = require( '@stdlib/utils/inmap-right' ); 41 ``` 42 43 #### inmapRight( collection, fcn\[, thisArg ] ) 44 45 Invokes a `function` for each element in a `collection` and updates the `collection` in-place, iterating from right to left. 46 47 ```javascript 48 function scale( value, index ) { 49 return value * index; 50 } 51 52 var arr = [ 1, 2, 3, 4 ]; 53 54 var out = inmapRight( arr, scale ); 55 // returns [ 0, 2, 6, 12 ] 56 57 var bool = ( out === arr ); 58 // returns true 59 ``` 60 61 The invoked `function` is provided three arguments: 62 63 - `value`: collection element 64 - `index`: collection index 65 - `collection`: input collection 66 67 Basic support for dynamic collections is provided. Note, however, that index incrementation is **not** guaranteed to be monotonically **decreasing**. 68 69 ```javascript 70 var arr = [ 1, 2, 3, 4 ]; 71 var i = 0; 72 73 function scale1( value, index, collection ) { 74 i += 1; 75 if ( index === 0 && collection.length < 10 ) { 76 collection.unshift( i+1 ); 77 } 78 return value * index; 79 } 80 81 var out = inmapRight( arr, scale1 ); 82 // returns [ 0, 0, 0, 0, 0, 0, 0, 2, 6, 12 ] 83 84 function scale2( value, index, collection ) { 85 collection.shift(); 86 return value * index; 87 } 88 89 arr = [ 1, 2, 3, 4 ]; 90 91 out = inmapRight( arr, scale2 ); 92 // returns [ 3, 12 ] 93 ``` 94 95 To set the function execution context, provide a `thisArg`. 96 97 ```javascript 98 function sum( value ) { 99 this.sum += value; 100 this.count += 1; 101 return value; 102 } 103 104 var arr = [ 1, 2, 3, 4 ]; 105 106 var context = { 107 'sum': 0, 108 'count': 0 109 }; 110 111 var out = inmapRight( arr, sum, context ); 112 // returns [ 1, 2, 3, 4 ] 113 114 var mean = context.sum / context.count; 115 // returns 2.5 116 ``` 117 118 </section> 119 120 <!-- /.usage --> 121 122 <!-- Package usage notes. Make sure to keep an empty line after the `section` element and another before the `/section` close. --> 123 124 <section class="notes"> 125 126 ## Notes 127 128 - A `collection` may be either an [`Array`][mdn-array], [`Typed Array`][mdn-typed-array], or an array-like [`Object`][mdn-object] (excluding `strings` and `functions`). 129 130 - The function differs from [`Array.prototype.map`][mdn-array-map] in the following ways: 131 132 - The function returns the input `collection`. 133 134 - The function modifies `collection` elements in-place. 135 136 - The function does **not** skip `undefined` elements. 137 138 <!-- eslint-disable no-sparse-arrays, stdlib/doctest-marker --> 139 140 ```javascript 141 function log( value, index ) { 142 console.log( '%s: %s', index, value ); 143 return value; 144 } 145 146 var arr = [ 1, , , 4 ]; 147 148 var out = inmapRight( arr, log ); 149 /* => 150 3: 4 151 2: undefined 152 1: undefined 153 0: 1 154 */ 155 ``` 156 157 - The function provides limited support for dynamic collections (i.e., collections whose `length` changes during execution). 158 159 </section> 160 161 <!-- /.notes --> 162 163 <!-- Package usage examples. --> 164 165 <section class="examples"> 166 167 ## Examples 168 169 <!-- eslint no-undef: "error" --> 170 171 ```javascript 172 var isEven = require( '@stdlib/assert/is-even' ).isPrimitive; 173 var inmapRight = require( '@stdlib/utils/inmap-right' ); 174 175 var bool; 176 var arr; 177 var out; 178 var i; 179 180 function scale( value, index, collection ) { 181 i += 1; 182 if ( isEven( i ) ) { 183 collection.pop(); 184 } else { 185 collection.unshift( i+1 ); 186 } 187 return value * index; 188 } 189 190 arr = new Array( 100 ); 191 for ( i = 0; i < arr.length; i++ ) { 192 arr[ i ] = i; 193 } 194 195 i = 0; 196 out = inmapRight( arr, scale ); 197 198 bool = ( out === arr ); 199 console.log( bool ); 200 201 console.log( out ); 202 ``` 203 204 </section> 205 206 <!-- /.examples --> 207 208 <!-- Section to include cited references. If references are included, add a horizontal rule *before* the section. Make sure to keep an empty line after the `section` element and another before the `/section` close. --> 209 210 <section class="references"> 211 212 </section> 213 214 <!-- /.references --> 215 216 <!-- Section for all links. Make sure to keep an empty line after the `section` element and another before the `/section` close. --> 217 218 <section class="links"> 219 220 [mdn-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array 221 222 [mdn-typed-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray 223 224 [mdn-object]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object 225 226 [mdn-array-map]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/map 227 228 </section> 229 230 <!-- /.links -->