@stdlib/strided-base-smskmap

Apply a unary function accepting and returning single-precision floating-point numbers to each element in a single-precision floating-point strided input array according to a corresponding element in a strided mask array and assign each result to an eleme

Usage no npm install needed!

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README

smskmap

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Apply a unary function accepting and returning single-precision floating-point numbers to each element in a single-precision floating-point strided input array according to a corresponding element in a strided mask array and assign each result to an element in a single-precision floating-point strided output array.

Installation

npm install @stdlib/strided-base-smskmap

Usage

var smskmap = require( '@stdlib/strided-base-smskmap' );

smskmap( N, x, strideX, mask, strideMask, y, strideY, fcn )

Applies a unary function accepting and returning single-precision floating-point numbers to each element in a single-precision floating-point strided input array according to a corresponding element in a strided mask array and assigns each result to an element in a single-precision floating-point strided output array.

var Float32Array = require( '@stdlib/array-float32' );
var Uint8Array = require( '@stdlib/array-uint8' );
var absf = require( '@stdlib/math-base-special-absf' );

var x = new Float32Array( [ -2.0, 1.0, -3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ] );
var m = new Uint8Array( [ 0, 0, 1, 0, 0, 1, 1, 0 ] );

// Compute the absolute values in-place:
smskmap( x.length, x, 1, m, 1, x, 1, absf );
// x => <Float32Array>[ 2.0, 1.0, -3.0, 5.0, 4.0, 0.0, -1.0, 3.0 ]

The function accepts the following arguments:

  • N: number of indexed elements.
  • x: input Float32Array.
  • strideX: index increment for x.
  • mask: mask Uint8Array.
  • strideMask: index increment for mask.
  • y: output Float32Array.
  • strideY: index increment for y.
  • fcn: function to apply.

The N and stride parameters determine which elements in the 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 Float32Array = require( '@stdlib/array-float32' );
var Uint8Array = require( '@stdlib/array-uint8' );
var floor = require( '@stdlib/math-base-special-floor' );
var absf = require( '@stdlib/math-base-special-absf' );

var x = new Float32Array( [ -1.0, -2.0, -3.0, -4.0, -5.0, -6.0 ] );
var m = new Uint8Array( [ 0, 0, 1, 0, 0, 1 ] );
var y = new Float32Array( [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ] );

var N = floor( x.length / 2 );

smskmap( N, x, 2, m, 2, y, -1, absf );
// y => <Float32Array>[ 5.0, 0.0, 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 Float32Array = require( '@stdlib/array-float32' );
var Uint8Array = require( '@stdlib/array-uint8' );
var floor = require( '@stdlib/math-base-special-floor' );
var absf = require( '@stdlib/math-base-special-absf' );

// Initial arrays...
var x0 = new Float32Array( [ -1.0, -2.0, -3.0, -4.0, -5.0, -6.0 ] );
var m0 = new Uint8Array( [ 0, 0, 1, 0, 0, 1 ] );
var y0 = new Float32Array( [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ] );

// Create offset views...
var x1 = new Float32Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element
var m1 = new Uint8Array( m0.buffer, m0.BYTES_PER_ELEMENT*3 ); // start at 4th element
var y1 = new Float32Array( y0.buffer, y0.BYTES_PER_ELEMENT*3 ); // start at 4th element

var N = floor( x0.length / 2 );

smskmap( N, x1, -2, m1, 1, y1, 1, absf );
// y0 => <Float32Array>[ 0.0, 0.0, 0.0, 6.0, 4.0, 0.0 ]

smskmap.ndarray( N, x, strideX, offsetX, mask, strideMask, offsetMask, y, strideY, offsetY, fcn )

Applies a unary function accepting and returning single-precision floating-point numbers to each element in a single-precision floating-point strided input array according to a corresponding element in a strided mask array and assigns each result to an element in a single-precision floating-point strided output array using alternative indexing semantics.

var Float32Array = require( '@stdlib/array-float32' );
var Uint8Array = require( '@stdlib/array-uint8' );
var absf = require( '@stdlib/math-base-special-absf' );

var x = new Float32Array( [ -1.0, -2.0, -3.0, -4.0, -5.0 ] );
var m = new Uint8Array( [ 0, 0, 1, 0, 0 ] );
var y = new Float32Array( [ 0.0, 0.0, 0.0, 0.0, 0.0 ] );

smskmap.ndarray( x.length, x, 1, 0, m, 1, 0, y, 1, 0, absf );
// y => <Float32Array>[ 1.0, 2.0, 0.0, 4.0, 5.0 ]

The function accepts the following additional arguments:

  • offsetX: starting index for x.
  • offsetMask: starting index for mask.
  • 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,

var Float32Array = require( '@stdlib/array-float32' );
var Uint8Array = require( '@stdlib/array-uint8' );
var floor = require( '@stdlib/math-base-special-floor' );
var absf = require( '@stdlib/math-base-special-absf' );

var x = new Float32Array( [ -1.0, -2.0, -3.0, -4.0, -5.0, -6.0 ] );
var m = new Uint8Array( [ 0, 0, 1, 0, 0, 1 ] );
var y = new Float32Array( [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ] );

var N = floor( x.length / 2 );

smskmap.ndarray( N, x, 2, 1, m, 2, 1, y, -1, y.length-1, absf );
// y => <Float32Array>[ 0.0, 0.0, 0.0, 0.0, 4.0, 2.0 ]

Examples

var round = require( '@stdlib/math-base-special-round' );
var randu = require( '@stdlib/random-base-randu' );
var bernoulli = require( '@stdlib/random-base-bernoulli' );
var Float32Array = require( '@stdlib/array-float32' );
var Uint8Array = require( '@stdlib/array-uint8' );
var smskmap = require( '@stdlib/strided-base-smskmap' );

function scale( x ) {
    return x * 10.0;
}

var x = new Float32Array( 10 );
var m = new Uint8Array( x.length );
var y = new Float32Array( x.length );

var i;
for ( i = 0; i < x.length; i++ ) {
    x[ i ] = round( (randu()*200.0) - 100.0 );
    m[ i ] = bernoulli( 0.2 );
}
console.log( x );
console.log( m );
console.log( y );

smskmap.ndarray( x.length, x, 1, 0, m, 1, 0, y, -1, y.length-1, scale );
console.log( y );

C APIs

Installation

npm install @stdlib/strided-base-smskmap

Usage

#include "stdlib/strided/base/smskmap.h"

stdlib_strided_smskmap( N, *X, strideX, *Mask, strideMask, *Y, strideY, fcn )

Applies a unary function accepting and returning single-precision floating-point numbers to each element in a single-precision floating-point strided input array according to a corresponding element in a strided mask array and assigns each result to an element in a single-precision floating-point strided output array.

#include <stdint.h>

static float scale( const float x ) {
    return x * 10.0f;
}

float X[] = { 1.0f, 2.0f, 3.0f, 4.0f, 5.0f, 6.0f };
uint8_t M[] = { 0, 0, 1, 0, 0, 1 };
float Y[] = { 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f };

int64_t N = 6;

stdlib_strided_smskmap( N, X, 1, M, 1, Y, 1, scale );

The function accepts the following arguments:

  • N: [in] int64_t number of indexed elements.
  • X: [in] float* input array.
  • strideX [in] int64_t index increment for X.
  • Mask: [in] uint8_t* mask array.
  • strideMask: [in] int64_t index increment for Mask.
  • Y: [out] float* output array.
  • strideY: [in] int64_t index increment for Y.
  • fcn: [in] float (*fcn)( float ) unary function to apply.
void stdlib_strided_smskmap( const int64_t N, const float *X, const int64_t strideX, const uint8_t *Mask, const int64_t strideMask, float *Y, const int64_t strideY, float (*fcn)( float ) );

Examples

#include "stdlib/strided/base/smskmap.h"
#include <stdint.h>
#include <stdio.h>
#include <inttypes.h>

// Define a callback:
static float scale( const float x ) {
    return x * 10.0f;
}

int main() {
    // Create an input strided array:
    float X[] = { 1.0f, 2.0f, 3.0f, 4.0f, 5.0f, 6.0f };

    // Create a mask strided array:
    uint8_t M[] = { 0, 0, 1, 0, 0, 1 };

    // Create an output strided array:
    float Y[] = { 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f };

    // Specify the number of elements:
    int64_t N = 6;

    // Define the strides:
    int64_t strideX = 1;
    int64_t strideM = 1;
    int64_t strideY = -1;

    // Apply the callback:
    stdlib_strided_smskmap( N, X, strideX, M, strideM, Y, strideY, scale );

    // Print the results:
    for ( int64_t i = 0; i < N; i++ ) {
        printf( "Y[ %"PRId64" ] = %f\n", i, Y[ i ] );
    }
}

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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License

See LICENSE.

Copyright

Copyright © 2016-2021. The Stdlib Authors.