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    @stdlib/stats-base-smeanwd
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    smeanwd

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    Calculate the arithmetic mean of a single-precision floating-point strided array using Welford's algorithm.

    The arithmetic mean is defined as

    Equation for the arithmetic mean.

    Installation

    npm install @stdlib/stats-base-smeanwd

    Usage

    var smeanwd = require( '@stdlib/stats-base-smeanwd' );

    smeanwd( N, x, stride )

    Computes the arithmetic mean of a single-precision floating-point strided array x using Welford's algorithm.

    var Float32Array = require( '@stdlib/array-float32' );
    
    var x = new Float32Array( [ 1.0, -2.0, 2.0 ] );
    var N = x.length;
    
    var v = smeanwd( N, x, 1 );
    // returns ~0.3333

    The function has the following parameters:

    • N: number of indexed elements.
    • x: input Float32Array.
    • stride: index increment for x.

    The N and stride parameters determine which elements in x are accessed at runtime. For example, to compute the arithmetic mean of every other element in x,

    var Float32Array = require( '@stdlib/array-float32' );
    var floor = require( '@stdlib/math-base-special-floor' );
    
    var x = new Float32Array( [ 1.0, 2.0, 2.0, -7.0, -2.0, 3.0, 4.0, 2.0 ] );
    var N = floor( x.length / 2 );
    
    var v = smeanwd( N, x, 2 );
    // returns 1.25

    Note that indexing is relative to the first index. To introduce an offset, use typed array views.

    var Float32Array = require( '@stdlib/array-float32' );
    var floor = require( '@stdlib/math-base-special-floor' );
    
    var x0 = new Float32Array( [ 2.0, 1.0, 2.0, -2.0, -2.0, 2.0, 3.0, 4.0 ] );
    var x1 = new Float32Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element
    
    var N = floor( x0.length / 2 );
    
    var v = smeanwd( N, x1, 2 );
    // returns 1.25

    smeanwd.ndarray( N, x, stride, offset )

    Computes the arithmetic mean of a single-precision floating-point strided array using Welford's algorithm and alternative indexing semantics.

    var Float32Array = require( '@stdlib/array-float32' );
    
    var x = new Float32Array( [ 1.0, -2.0, 2.0 ] );
    var N = x.length;
    
    var v = smeanwd.ndarray( N, x, 1, 0 );
    // returns ~0.33333

    The function has the following additional parameters:

    • offset: starting index for x.

    While 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 for every other value in x starting from the second value

    var Float32Array = require( '@stdlib/array-float32' );
    var floor = require( '@stdlib/math-base-special-floor' );
    
    var x = new Float32Array( [ 2.0, 1.0, 2.0, -2.0, -2.0, 2.0, 3.0, 4.0 ] );
    var N = floor( x.length / 2 );
    
    var v = smeanwd.ndarray( N, x, 2, 1 );
    // returns 1.25

    Notes

    • If N <= 0, both functions return NaN.

    Examples

    var randu = require( '@stdlib/random-base-randu' );
    var round = require( '@stdlib/math-base-special-round' );
    var Float32Array = require( '@stdlib/array-float32' );
    var smeanwd = require( '@stdlib/stats-base-smeanwd' );
    
    var x;
    var i;
    
    x = new Float32Array( 10 );
    for ( i = 0; i < x.length; i++ ) {
        x[ i ] = round( (randu()*100.0) - 50.0 );
    }
    console.log( x );
    
    var v = smeanwd( x.length, x, 1 );
    console.log( v );

    References

    • Welford, B. P. 1962. "Note on a Method for Calculating Corrected Sums of Squares and Products." Technometrics 4 (3). Taylor & Francis: 419–20. doi:10.1080/00401706.1962.10490022.
    • van Reeken, A. J. 1968. "Letters to the Editor: Dealing with Neely's Algorithms." Communications of the ACM 11 (3): 149–50. doi:10.1145/362929.362961.

    Notice

    This package is part of stdlib, a standard library for JavaScript and Node.js, with an emphasis on numerical and scientific computing. The library provides a collection of robust, high performance libraries for mathematics, statistics, streams, utilities, and more.

    For more information on the project, filing bug reports and feature requests, and guidance on how to develop stdlib, see the main project repository.

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    License

    See LICENSE.

    Copyright

    Copyright © 2016-2021. The Stdlib Authors.

    Install

    npm i @stdlib/stats-base-smeanwd

    Homepage

    stdlib.io

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    5

    Version

    0.0.5

    License

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    77.4 kB

    Total Files

    21

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