# @stdlib/math-strided-special-abs2-by

0.2.0 • Public • Published

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# abs2By

Compute the squared absolute value of each element retrieved from an input strided array via a callback function.

## Installation

`npm install @stdlib/math-strided-special-abs2-by`

## Usage

`var abs2By = require( '@stdlib/math-strided-special-abs2-by' );`

#### abs2By( N, x, strideX, y, strideY, clbk[, thisArg] )

Computes the squared absolute value of each element retrieved from an input strided array `x` via a callback function and assigns each result to an element in an output strided array `y`.

```function accessor( v ) {
return v;
}

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

abs2By( x.length, x, 1, y, 1, accessor );
// y => [ 1.0, 4.0, 9.0, 16.0, 25.0 ]```

The function accepts the following arguments:

The invoked callback function is provided six arguments:

• value: input array element.
• idx: iteration index (zero-based).
• xi: input array strided index (`offsetX + idx*strideX`).
• yi: output array strided index (`offsetY + idx*strideY`).
• x: input array/collection.
• y: output array/collection.

To set the callback execution context, provide a `thisArg`.

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

var context = {
'count': 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 ];

abs2By( x.length, x, 1, y, 1, accessor, context );
// y => [ 1.0, 4.0, 9.0, 16.0, 25.0 ]

var cnt = context.count;
// returns 5```

The `N` and `stride` parameters determine which elements in `x` and `y` 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,

```function accessor( v ) {
return v;
}

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 ];

abs2By( 3, x, 2, y, -1, accessor );
// y => [ 25.0, 9.0, 1.0, 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' );

function accessor( v ) {
return v;
}

// 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

abs2By( 3, x1, -2, y1, 1, accessor );
// y0 => <Float64Array>[ 0.0, 0.0, 0.0, 36.0, 16.0, 4.0 ]```

#### abs2By.ndarray( N, x, strideX, offsetX, y, strideY, offsetY, clbk[, thisArg] )

Computes the squared absolute value of each element retrieved from an input strided array `x` via a callback function and assigns each result to an element in an output strided array `y` using alternative indexing semantics.

```function accessor( v ) {
return v;
}

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

abs2By.ndarray( x.length, x, 1, 0, y, 1, 0, accessor );
// y => [ 1.0, 4.0, 9.0, 16.0, 25.0 ]```

The function accepts the following additional arguments:

• offsetX: starting index for `x`.
• offsetY: starting index for `y`.

While `typed array` views mandate a view offset based on the underlying `buffer`, the `offsetX` and `offsetY` parameters support 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`,

```function accessor( v ) {
return v;
}

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 ];

abs2By.ndarray( 3, x, 2, 1, y, -1, y.length-1, accessor );
// y => [ 0.0, 0.0, 0.0, 36.0, 16.0, 4.0 ]```

## Notes

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

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

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

abs2By( x.length, x, 1, y, 1, accessor );
// y => [ 0.0, 0.0, 0.0, 0.0, 0.0 ]```

## Examples

```var uniform = require( '@stdlib/random-base-uniform' ).factory
var filledarray = require( '@stdlib/array-filled' );
var filledarrayBy = require( '@stdlib/array-filled-by' );
var abs2By = require( '@stdlib/math-strided-special-abs2-by' );

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

var x = filledarrayBy( 10, 'generic', uniform( -10.0, 10.0 ) );
console.log( x );

var y = filledarray( null, 10, 'generic' );
console.log( y );

abs2By.ndarray( x.length, x, 1, 0, y, -1, y.length-1, 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.

## Package Sidebar

### Install

`npm i @stdlib/math-strided-special-abs2-by`

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