README.md (4935B)
1 <!-- 2 3 @license Apache-2.0 4 5 Copyright (c) 2020 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 # Nullary 22 23 > Apply a nullary callback and assign results to elements in a strided output array. 24 25 <section class="intro"> 26 27 </section> 28 29 <!-- /.intro --> 30 31 <section class="usage"> 32 33 ## Usage 34 35 ```javascript 36 var nullary = require( '@stdlib/strided/base/nullary' ); 37 ``` 38 39 #### nullary( arrays, shape, strides, fcn ) 40 41 Applies a nullary callback and assigns results to elements in a strided output array. 42 43 ```javascript 44 var Float64Array = require( '@stdlib/array/float64' ); 45 46 function fill() { 47 return 3.0; 48 } 49 50 var x = new Float64Array( [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ] ); 51 52 nullary( [ x ], [ x.length ], [ 1 ], fill ); 53 // x => <Float64Array>[ 3.0, 3.0, 3.0, 3.0, 3.0, 3.0, 3.0, 3.0 ] 54 ``` 55 56 The function accepts the following arguments: 57 58 - **arrays**: array-like object containing one strided output array. 59 - **shape**: array-like object containing a single element, the number of indexed elements. 60 - **strides**: array-like object containing the stride length for the strided output array. 61 - **fcn**: nullary function to apply. 62 63 The `shape` and `strides` parameters determine which elements in the strided output array are accessed at runtime. For example, to index the first `N` elements of the strided output array in reverse order, 64 65 ```javascript 66 var Float64Array = require( '@stdlib/array/float64' ); 67 var floor = require( '@stdlib/math/base/special/floor' ); 68 69 function fill() { 70 return 3.0; 71 } 72 73 var x = new Float64Array( [ -1.0, -2.0, -3.0, -4.0, -5.0, -6.0 ] ); 74 var N = floor( x.length / 2 ); 75 76 nullary( [ x ], [ N ], [ -1 ], fill ); 77 // x => <Float64Array>[ 3.0, 3.0, 3.0, -4.0, -5.0, -6.0 ] 78 ``` 79 80 Note that indexing is relative to the first index. To introduce an offset, use [`typed array`][mdn-typed-array] views. 81 82 ```javascript 83 var Float64Array = require( '@stdlib/array/float64' ); 84 var floor = require( '@stdlib/math/base/special/floor' ); 85 86 function fill() { 87 return 3.0; 88 } 89 90 // Initial arrays... 91 var x0 = new Float64Array( [ -1.0, -2.0, -3.0, -4.0, -5.0, -6.0 ] ); 92 93 // Create offset views... 94 var x1 = new Float64Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element 95 96 var N = floor( x0.length / 2 ); 97 98 nullary( [ x1 ], [ N ], [ 1 ], fill ); 99 // x0 => <Float64Array>[ -1.0, 3.0, -3.0, 3.0, -5.0, 3.0 ] 100 ``` 101 102 #### nullary.ndarray( arrays, shape, strides, offsets, fcn ) 103 104 Applies a nullary callback and assigns results to elements in a strided output array using alternative indexing semantics. 105 106 ```javascript 107 var Float64Array = require( '@stdlib/array/float64' ); 108 109 function fill() { 110 return 3.0; 111 } 112 113 var x = new Float64Array( [ -1.0, -2.0, -3.0, -4.0, -5.0 ] ); 114 115 nullary.ndarray( [ x ], [ x.length ], [ 1 ], [ 0 ], fill ); 116 // x => <Float64Array>[ 3.0, 3.0, 3.0, 3.0, 3.0 ] 117 ``` 118 119 The function accepts the following additional arguments: 120 121 - **offsets**: array-like object containing the starting index (i.e., index offset) for the strided output array. 122 123 While [`typed array`][mdn-typed-array] views mandate a view offset based on the underlying `buffer`, the `offsets` parameter supports indexing semantics based on starting indices. For example, to index the last `N` elements in the strided output array, 124 125 ```javascript 126 var Float64Array = require( '@stdlib/array/float64' ); 127 var floor = require( '@stdlib/math/base/special/floor' ); 128 129 function fill() { 130 return 3.0; 131 } 132 133 var x = new Float64Array( [ -1.0, -2.0, -3.0, -4.0, -5.0, -6.0 ] ); 134 var N = floor( x.length / 2 ); 135 136 nullary.ndarray( [ x ], [ N ], [ -1 ], [ x.length-1 ], fill ); 137 // x => <Float64Array>[ -1.0, -2.0, -3.0, 3.0, 3.0, 3.0 ] 138 ``` 139 140 </section> 141 142 <!-- /.usage --> 143 144 <section class="notes"> 145 146 </section> 147 148 <!-- /.notes --> 149 150 <section class="examples"> 151 152 ## Examples 153 154 <!-- eslint no-undef: "error" --> 155 156 ```javascript 157 var discreteUniform = require( '@stdlib/random/base/discrete-uniform' ).factory; 158 var filledarray = require( '@stdlib/array/filled' ); 159 var nullary = require( '@stdlib/strided/base/nullary' ); 160 161 var N = 10; 162 163 var x = filledarray( 0.0, N, 'generic' ); 164 console.log( x ); 165 166 var shape = [ N ]; 167 var strides = [ 1 ]; 168 var offsets = [ 0 ]; 169 170 nullary.ndarray( [ x ], shape, strides, offsets, discreteUniform( -100, 100 ) ); 171 console.log( x ); 172 ``` 173 174 </section> 175 176 <!-- /.examples --> 177 178 <section class="links"> 179 180 [mdn-typed-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray 181 182 </section> 183 184 <!-- /.links -->