dmeanli.js (1857B)
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 dapxsum = require( '@stdlib/blas/ext/base/dapxsum' ).ndarray; 24 25 26 // MAIN // 27 28 /** 29 * Computes the arithmetic mean of a double-precision floating-point strided array using a one-pass trial mean algorithm. 30 * 31 * ## References 32 * 33 * - 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). 34 * 35 * @param {PositiveInteger} N - number of indexed elements 36 * @param {Float64Array} x - input array 37 * @param {integer} stride - stride length 38 * @returns {number} arithmetic mean 39 * 40 * @example 41 * var Float64Array = require( '@stdlib/array/float64' ); 42 * 43 * var x = new Float64Array( [ 1.0, -2.0, 2.0 ] ); 44 * var N = x.length; 45 * 46 * var v = dmeanli( N, x, 1 ); 47 * // returns ~0.3333 48 */ 49 function dmeanli( N, x, stride ) { 50 var ix; 51 52 if ( N <= 0 ) { 53 return NaN; 54 } 55 if ( N === 1 || stride === 0 ) { 56 return x[ 0 ]; 57 } 58 if ( stride < 0 ) { 59 ix = (1-N) * stride; 60 } else { 61 ix = 0; 62 } 63 return x[ ix ] + ( dapxsum( N-1, -x[ ix ], x, stride, ix+stride ) / N ); 64 } 65 66 67 // EXPORTS // 68 69 module.exports = dmeanli;