@stdlib/stats-strided-nanmaxabs

v0.1.1

Published

a month ago

Calculate the maximum absolute value of a strided array, ignoring NaN values.

nanmaxabs

Calculate the maximum absolute value of a strided array, ignoring NaN values.

Installation

npm install @stdlib/stats-strided-nanmaxabs

Usage

var nanmaxabs = require( '@stdlib/stats-strided-nanmaxabs' );

nanmaxabs( N, x, strideX )

Computes the maximum absolute value of a strided array, ignoring NaN values.

var x = [ 1.0, -2.0, NaN, 2.0 ];

var v = nanmaxabs( x.length, x, 1 );
// returns 2.0

The function has the following parameters:

N: number of indexed elements.
x: input Array or typed array.
strideX: stride length for x.

The N and stride parameters determine which elements in the strided array are accessed at runtime. For example, to compute the maximum absolute value of every other element in x,

var x = [ 1.0, 2.0, 2.0, -7.0, -2.0, 3.0, 4.0, 2.0, NaN, NaN ];

var v = nanmaxabs( 5, x, 2 );
// returns 4.0

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

var Float64Array = require( '@stdlib/array-float64' );

var x0 = new Float64Array( [ 2.0, 1.0, 2.0, -2.0, -2.0, NaN, NaN, 4.0 ] );
var x1 = new Float64Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element

var v = nanmaxabs( 4, x1, 2 );
// returns 4.0

nanmaxabs.ndarray( N, x, strideX, offsetX )

Computes the maximum absolute value of a strided array, ignoring NaN values and using alternative indexing semantics.

var x = [ 1.0, -2.0, NaN, 2.0 ];

var v = nanmaxabs.ndarray( x.length, x, 1, 0 );
// returns 2.0

The function has the following additional parameters:

offsetX: 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 maximum absolute value for every other element in x starting from the second element

var x = [ 2.0, 1.0, 2.0, -2.0, -2.0, NaN, NaN, 2.0, 3.0, 4.0 ];

var v = nanmaxabs.ndarray( 5, x, 2, 1 );
// returns 4.0

Notes

If N <= 0, both functions return NaN.
Both functions support array-like objects having getter and setter accessors for array element access (e.g., @stdlib/array-base/accessor).
Depending on the environment, the typed versions (dnanmaxabs, snanmaxabs, etc.) are likely to be significantly more performant.

Examples

var uniform = require( '@stdlib/random-base-uniform' );
var filledarrayBy = require( '@stdlib/array-filled-by' );
var bernoulli = require( '@stdlib/random-base-bernoulli' );
var nanmaxabs = require( '@stdlib/stats-strided-nanmaxabs' );

function rand() {
    if ( bernoulli( 0.8 ) < 1 ) {
        return NaN;
    }
    return uniform( -50.0, 50.0 );
}

var x = filledarrayBy( 10, 'float64', rand );
console.log( x );

var v = nanmaxabs( x.length, x, 1 );
console.log( v );

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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See LICENSE.

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