@stdlib/blas-ext-base-gfill-by NPM

gfillBy

Fill a strided array according to a provided callback function.

Installation

npm install @stdlib/blas-ext-base-gfill-by

Usage

var gfillBy = require( '@stdlib/blas-ext-base-gfill-by' );

gfillBy( N, x, stride, clbk[, thisArg] )

Fills a strided array x according to a provided callback function.

function fill( v, i ) {
    return v * i;
}

var x = [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ];

gfillBy( x.length, x, 1, fill );
// x => [ 0.0, 1.0, 6.0, -15.0, 16.0, 0.0, -6.0, -21.0 ]

The function has the following parameters:

N: number of indexed elements.
x: input array.
stride: index increment.
clbk: callback function.
thisArg: execution context (optional).

The invoked callback is provided four arguments:

value: array element.
aidx: array index.
sidx: strided index (offset + aidx*stride).
array: input array/collection.

To set the callback execution context, provide a thisArg.

function fill( v, i ) {
    this.count += 1;
    return v * i;
}

var x = [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ];

var context = {
    'count': 0
};

gfillBy( x.length, x, 1, fill, context );
// x => [ 0.0, 1.0, 6.0, -15.0, 16.0, 0.0, -6.0, -21.0 ]

var cnt = context.count;
// returns 8

The N and stride parameters determine which elements in x are accessed at runtime. For example, to fill every other element

var floor = require( '@stdlib/math-base-special-floor' );

function fill( v, i ) {
    return v * i;
}

var x = [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ];
var N = floor( x.length / 2 );

gfillBy( N, x, 2, fill );
// x => [ 0.0, 1.0, 3.0, -5.0, 8.0, 0.0, -3.0, -3.0 ]

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

var Float64Array = require( '@stdlib/array-float64' );
var floor = require( '@stdlib/math-base-special-floor' );

function fill( v, i ) {
    return v * i;
}

// Initial array...
var x0 = new Float64Array( [ 1.0, -2.0, 3.0, -4.0, 5.0, -6.0 ] );

// Create an offset view...
var x1 = new Float64Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element
var N = floor( x0.length/2 );

// Fill every other element...
gfillBy( N, x1, 2, fill );
// x0 => <Float64Array>[ 1.0, 0.0, 3.0, -4.0, 5.0, -12.0 ]

gfillBy.ndarray( N, x, stride, offset, clbk[, thisArg] )

Fills a strided array x according to a provided callback function and using alternative indexing semantics.

function fill( v, i ) {
    return v * i;
}

var x = [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ];

gfillBy.ndarray( x.length, x, 1, 0, fill );
// x => [ 0.0, 1.0, 6.0, -15.0, 16.0, 0.0, -6.0, -21.0 ]

The function has the following additional parameters:

offset: starting index.

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 access only the last three elements of x

function fill( v, i ) {
    return v * i;
}

var x = [ 1.0, -2.0, 3.0, -4.0, 5.0, -6.0 ];

gfillBy.ndarray( 3, x, 1, x.length-3, fill );
// x => [ 1.0, -2.0, 3.0, 0.0, 5.0, -12.0 ]

Notes

If N <= 0, both functions return x unchanged.
Both functions support array-like objects having getter and setter accessors for array element access (e.g., @stdlib/array-complex64).
When filling a strided array with a scalar constant, prefer using dfill, sfill, and/or gfill, as, depending on the environment, these interfaces are likely to be significantly more performant.

Examples

var round = require( '@stdlib/math-base-special-round' );
var randu = require( '@stdlib/random-base-randu' );
var Float64Array = require( '@stdlib/array-float64' );
var gfillBy = require( '@stdlib/blas-ext-base-gfill-by' );

function fill() {
    var rand = round( randu()*100.0 );
    var sign = randu();
    if ( sign < 0.5 ) {
        sign = -1.0;
    } else {
        sign = 1.0;
    }
    return sign * rand;
}

var x = new Float64Array( 10 );
console.log( x );

gfillBy( x.length, x, 1, fill );
console.log( x );

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.