@stdlib/strided-base-unary-by NPM

unaryBy

Apply a unary function to each element retrieved from a strided input array according to a callback function and assign results to a strided output array.

Installation

npm install @stdlib/strided-base-unary-by

Usage

var unaryBy = require( '@stdlib/strided-base-unary-by' );

unaryBy( arrays, shape, strides, fcn, clbk[, thisArg] )

Applies a unary function to each element retrieved from a strided input array according to a callback function and assigns results to a strided output array.

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

function accessor( v ) {
    return v * 2.0;
}

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

unaryBy( [ x, y ], [ x.length ], [ 1, 1 ], abs, accessor );
// y => [ 4.0, 2.0, 6.0, 10.0, 8.0, 0.0, 2.0, 6.0 ]

The function accepts the following arguments:

arrays: array-like object containing one strided input array and one strided output array.
shape: array-like object containing a single element, the number of indexed elements.
strides: array-like object containing the stride lengths for the strided input and output arrays.
fcn: unary function to apply to callback return values.
clbk: callback function.
thisArg: execution context (optional).

The invoked callback function is provided four arguments:

value: input array element.
idx: iteration index (zero-based).
indices: input and output array strided indices [ix, iy] (computed according to offset + idx*stride).
arrays: input and output arrays/collections [x, y].

To set the callback execution context, provide a thisArg.

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

function accessor( v ) {
    this.count += 1;
    return v * 2.0;
}

var context = {
    'count': 0
};

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

unaryBy( [ x, y ], [ x.length ], [ 1, 1 ], abs, accessor, context );
// y => [ 4.0, 2.0, 6.0, 10.0, 8.0, 0.0, 2.0, 6.0 ]

var cnt = context.count;
// returns 8

The shape and stride parameters determine which elements in the input and output strided arrays are accessed at runtime. For example, to index every other value in x and to index the first N elements of y in reverse order,

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

function accessor( v ) {
    return v * 2.0;
}

var x = [ -1.0, -2.0, -3.0, -4.0, -5.0, -6.0 ];
var y = [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ];

unaryBy( [ x, y ], [ 3 ], [ 2, -1 ], abs, accessor );
// y => [ 10.0, 6.0, 2.0, 0.0, 0.0, 0.0 ]

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

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

function accessor( v ) {
    return v * 2.0;
}

// Initial arrays...
var x0 = new Float64Array( [ -1.0, -2.0, -3.0, -4.0, -5.0, -6.0 ] );
var y0 = new Float64Array( [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ] );

// Create offset views...
var x1 = new Float64Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element
var y1 = new Float64Array( y0.buffer, y0.BYTES_PER_ELEMENT*3 ); // start at 4th element

unaryBy( [ x1, y1 ], [ 3 ], [ -2, 1 ], abs, accessor );
// y0 => <Float64Array>[ 0.0, 0.0, 0.0, 12.0, 8.0, 4.0 ]

unaryBy.ndarray( arrays, shape, strides, offsets, fcn, clbk[, thisArg] )

Applies a unary function to each element retrieved from a strided input array according to a callback function and assigns results to a strided output array using alternative indexing semantics.

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

function accessor( v ) {
    return v * 2.0;
}

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

unaryBy.ndarray( [ x, y ], [ x.length ], [ 1, 1 ], [ 0, 0 ], abs, accessor );
// y => [ 2.0, 4.0, 6.0, 8.0, 10.0 ]

The function accepts the following additional arguments:

offsets: array-like object containing the starting indices (i.e., index offsets) for the strided input and output arrays.

While typed array views mandate a view offset based on the underlying buffer, the offsets parameter supports indexing semantics based on starting indices. For example, to index every other value in x starting from the second value and to index the last N elements in y in reverse order,

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

function accessor( v ) {
    return v * 2.0;
}

var x = [ -1.0, -2.0, -3.0, -4.0, -5.0, -6.0 ];
var y = [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ];

unaryBy.ndarray( [ x, y ], [ 3 ], [ 2, -1 ], [ 1, y.length-1 ], abs, accessor );
// y => [ 0.0, 0.0, 0.0, 12.0, 8.0, 4.0 ]

Notes

If a provided callback function does not return any value (or equivalently, explicitly returns undefined), the value is ignored.

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

function accessor() {
    // No-op...
}

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

unaryBy( [ x, y ], [ x.length ], [ 1, 1 ], abs, accessor );
// y => [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ]

Examples

var discreteUniform = require( '@stdlib/random-base-discrete-uniform' ).factory;
var filledarray = require( '@stdlib/array-filled' );
var filledarrayBy = require( '@stdlib/array-filled-by' );
var abs = require( '@stdlib/math-base-special-abs' );
var unaryBy = require( '@stdlib/strided-base-unary-by' );

function accessor( v, i ) {
    if ( (i%3) === 0 ) {
        // Simulate a "missing" value...
        return;
    }
    return v;
}

var N = 10;

var x = filledarrayBy( N, 'generic', discreteUniform( -100, 100 ) );
console.log( x );

var y = filledarray( null, N, 'generic' );
console.log( y );

var shape = [ N ];
var strides = [ 1, -1 ];
var offsets = [ 0, N-1 ];

unaryBy.ndarray( [ x, y ], shape, strides, offsets, abs, accessor );
console.log( y );

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.