README.md (5360B)
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 # nanmean 22 23 > Calculate the [arithmetic mean][arithmetic-mean] of a strided array, ignoring `NaN` values. 24 25 <section class="intro"> 26 27 The [arithmetic mean][arithmetic-mean] is defined as 28 29 <!-- <equation class="equation" label="eq:arithmetic_mean" align="center" raw="\mu = \frac{1}{n} \sum_{i=0}^{n-1} x_i" alt="Equation for the arithmetic mean."> --> 30 31 <div class="equation" align="center" data-raw-text="\mu = \frac{1}{n} \sum_{i=0}^{n-1} x_i" data-equation="eq:arithmetic_mean"> 32 <img src="https://cdn.jsdelivr.net/gh/stdlib-js/stdlib@3d4f5555000c9418c73d1011bcbc3a93f477935e/lib/node_modules/@stdlib/stats/base/nanmean/docs/img/equation_arithmetic_mean.svg" alt="Equation for the arithmetic mean."> 33 <br> 34 </div> 35 36 <!-- </equation> --> 37 38 </section> 39 40 <!-- /.intro --> 41 42 <section class="usage"> 43 44 ## Usage 45 46 ```javascript 47 var nanmean = require( '@stdlib/stats/base/nanmean' ); 48 ``` 49 50 #### nanmean( N, x, stride ) 51 52 Computes the [arithmetic mean][arithmetic-mean] of a strided array `x`, ignoring `NaN` values. 53 54 ```javascript 55 var x = [ 1.0, -2.0, NaN, 2.0 ]; 56 var N = x.length; 57 58 var v = nanmean( N, x, 1 ); 59 // returns ~0.3333 60 ``` 61 62 The function has the following parameters: 63 64 - **N**: number of indexed elements. 65 - **x**: input [`Array`][mdn-array] or [`typed array`][mdn-typed-array]. 66 - **stride**: index increment for `x`. 67 68 The `N` and `stride` parameters determine which elements in `x` are accessed at runtime. For example, to compute the [arithmetic mean][arithmetic-mean] of every other element in `x`, 69 70 ```javascript 71 var floor = require( '@stdlib/math/base/special/floor' ); 72 73 var x = [ 1.0, 2.0, 2.0, -7.0, -2.0, 3.0, 4.0, 2.0, NaN ]; 74 var N = floor( x.length / 2 ); 75 76 var v = nanmean( N, x, 2 ); 77 // returns 1.25 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 <!-- eslint-disable stdlib/capitalized-comments --> 83 84 ```javascript 85 var Float64Array = require( '@stdlib/array/float64' ); 86 var floor = require( '@stdlib/math/base/special/floor' ); 87 88 var x0 = new Float64Array( [ 2.0, 1.0, 2.0, -2.0, -2.0, 2.0, 3.0, 4.0, NaN ] ); 89 var x1 = new Float64Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element 90 91 var N = floor( x0.length / 2 ); 92 93 var v = nanmean( N, x1, 2 ); 94 // returns 1.25 95 ``` 96 97 #### nanmean.ndarray( N, x, stride, offset ) 98 99 Computes the [arithmetic mean][arithmetic-mean] of a strided array, ignoring `NaN` values and using alternative indexing semantics. 100 101 ```javascript 102 var x = [ 1.0, -2.0, NaN, 2.0 ]; 103 var N = x.length; 104 105 var v = nanmean.ndarray( N, x, 1, 0 ); 106 // returns ~0.33333 107 ``` 108 109 The function has the following additional parameters: 110 111 - **offset**: starting index for `x`. 112 113 While [`typed array`][mdn-typed-array] views mandate a view offset based on the underlying `buffer`, the `offset` parameter supports indexing semantics based on a starting index. For example, to calculate the [arithmetic mean][arithmetic-mean] for every other value in `x` starting from the second value 114 115 ```javascript 116 var floor = require( '@stdlib/math/base/special/floor' ); 117 118 var x = [ 2.0, 1.0, 2.0, -2.0, -2.0, 2.0, 3.0, 4.0, NaN ]; 119 var N = floor( x.length / 2 ); 120 121 var v = nanmean.ndarray( N, x, 2, 1 ); 122 // returns 1.25 123 ``` 124 125 </section> 126 127 <!-- /.usage --> 128 129 <section class="notes"> 130 131 ## Notes 132 133 - If `N <= 0`, both functions return `NaN`. 134 - If every indexed element is `NaN`, both functions return `NaN`. 135 - Depending on the environment, the typed versions ([`dnanmean`][@stdlib/stats/base/dnanmean], [`snanmean`][@stdlib/stats/base/snanmean], etc.) are likely to be significantly more performant. 136 137 </section> 138 139 <!-- /.notes --> 140 141 <section class="examples"> 142 143 ## Examples 144 145 <!-- eslint no-undef: "error" --> 146 147 ```javascript 148 var randu = require( '@stdlib/random/base/randu' ); 149 var round = require( '@stdlib/math/base/special/round' ); 150 var Float64Array = require( '@stdlib/array/float64' ); 151 var nanmean = require( '@stdlib/stats/base/nanmean' ); 152 153 var x; 154 var i; 155 156 x = new Float64Array( 10 ); 157 for ( i = 0; i < x.length; i++ ) { 158 if ( randu() < 0.2 ) { 159 x[ i ] = NaN; 160 } else { 161 x[ i ] = round( (randu()*100.0) - 50.0 ); 162 } 163 } 164 console.log( x ); 165 166 var v = nanmean( x.length, x, 1 ); 167 console.log( v ); 168 ``` 169 170 </section> 171 172 <!-- /.examples --> 173 174 <section class="links"> 175 176 [arithmetic-mean]: https://en.wikipedia.org/wiki/Arithmetic_mean 177 178 [mdn-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array 179 180 [mdn-typed-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray 181 182 [@stdlib/stats/base/dnanmean]: https://www.npmjs.com/package/@stdlib/stats/tree/main/base/dnanmean 183 184 [@stdlib/stats/base/snanmean]: https://www.npmjs.com/package/@stdlib/stats/tree/main/base/snanmean 185 186 </section> 187 188 <!-- /.links -->