smeanli.js (2000B)
1 /** 2 * @license Apache-2.0 3 * 4 * Copyright (c) 2020 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 float64ToFloat32 = require( '@stdlib/number/float64/base/to-float32' ); 24 var sapxsum = require( '@stdlib/blas/ext/base/sapxsum' ).ndarray; 25 26 27 // MAIN // 28 29 /** 30 * Computes the arithmetic mean of a single-precision floating-point strided array using a one-pass trial mean algorithm. 31 * 32 * ## References 33 * 34 * - Ling, Robert F. 1974. "Comparison of Several Algorithms for Computing Sample Means and Variances." _Journal of the American Statistical Association_ 69 (348). American Statistical Association, Taylor & Francis, Ltd.: 859–66. doi:[10.2307/2286154](https://doi.org/10.2307/2286154). 35 * 36 * @param {PositiveInteger} N - number of indexed elements 37 * @param {Float32Array} x - input array 38 * @param {integer} stride - stride length 39 * @returns {number} arithmetic mean 40 * 41 * @example 42 * var Float32Array = require( '@stdlib/array/float32' ); 43 * 44 * var x = new Float32Array( [ 1.0, -2.0, 2.0 ] ); 45 * var N = x.length; 46 * 47 * var v = smeanli( N, x, 1 ); 48 * // returns ~0.3333 49 */ 50 function smeanli( N, x, stride ) { 51 var ix; 52 53 if ( N <= 0 ) { 54 return NaN; 55 } 56 if ( N === 1 || stride === 0 ) { 57 return x[ 0 ]; 58 } 59 if ( stride < 0 ) { 60 ix = (1-N) * stride; 61 } else { 62 ix = 0; 63 } 64 return float64ToFloat32( x[ ix ] + float64ToFloat32( sapxsum( N-1, -x[ ix ], x, stride, ix+stride ) / N ) ); // eslint-disable-line max-len 65 } 66 67 68 // EXPORTS // 69 70 module.exports = smeanli;