gfillBy

Fill a strided array according to a provided callback function.

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 );