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readDataView

Copy elements from an input strided DataView to elements in an output strided array.

Installation

npm install @stdlib/strided-base-read-dataview

Alternatively,

• To load the package in a website via a script tag without installation and bundlers, use the ES Module available on the esm branch (see README).
• If you are using Deno, visit the deno branch (see README for usage intructions).
• For use in Observable, or in browser/node environments, use the Universal Module Definition (UMD) build available on the umd branch (see README).

The branches.md file summarizes the available branches and displays a diagram illustrating their relationships.

To view installation and usage instructions specific to each branch build, be sure to explicitly navigate to the respective README files on each branch, as linked to above.

Usage

var readDataView = require( '@stdlib/strided-base-read-dataview' );

readDataView( N, view, strideView, out, strideOut, littleEndian )

Copies elements from an input strided DataView to elements in an output strided array.

var Float64Array = require( '@stdlib/array-float64' );
var DataView = require( '@stdlib/array-dataview' );

var x = new Float64Array( [ 1.0, 2.0, 3.0, 4.0 ] );
var view = new DataView( x.buffer );

var y = new Float64Array( x.length );
var out = readDataView( x.length, view, 8, y, 1, true );
// e.g., returns <Float64Array>[ 1.0, 2.0, 3.0, 4.0 ]

var bool = ( out === y );
// returns true

The function accepts the following arguments:

• N: number of indexed elements.
• view: input DataView.
• strideView: index increment (in bytes) for view.
• out: output strided array.
• strideOut: index increment for out.
• littleEndian: boolean indicating whether to store values in little-endian format.

The N and stride parameters determine which elements in view and out are accessed at runtime. For example, to index the first N elements of view in reverse order and to index every other value in out,

var Float64Array = require( '@stdlib/array-float64' );
var DataView = require( '@stdlib/array-dataview' );

var x = new Float64Array( [ 1.0, 2.0, 3.0, 4.0 ] );
var view = new DataView( x.buffer );

var y = new Float64Array( x.length*2 );
var out = readDataView( x.length, view, -8, y, 2, true );
// e.g., returns <Float64Array>[ 4.0, 0.0, 3.0, 0.0, 2.0, 0.0, 1.0, 0.0 ]

var bool = ( out === y );
// returns true

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

var Float64Array = require( '@stdlib/array-float64' );
var DataView = require( '@stdlib/array-dataview' );

var x = new Float64Array( [ 1.0, 2.0, 3.0, 4.0 ] );
var view = new DataView( x.buffer );

// Initial output array:
var y0 = new Float64Array( x.length+1 );

// Create an offset view:
var y1 = new Float64Array( y0.buffer, y0.BYTES_PER_ELEMENT*1 ); // start at 2nd element

var out = readDataView( x.length, view, 8, y1, 1, true );
// e.g., returns <Float64Array>[ 1.0, 2.0, 3.0, 4.0 ]

var bool = ( out === y1 );
// returns true

readDataView.ndarray( N, view, strideView, offsetView, out, strideOut, offsetOut, littleEndian )

Copies elements from an input strided DataView to elements in an output strided array using alternative indexing semantics.

var Float64Array = require( '@stdlib/array-float64' );
var DataView = require( '@stdlib/array-dataview' );

var x = new Float64Array( [ 1.0, 2.0, 3.0, 4.0 ] );
var view = new DataView( x.buffer );

var y = new Float64Array( x.length );
var out = readDataView.ndarray( x.length, view, 8, 0, y, 1, 0, true );
// e.g., returns <Float64Array>[ 1.0, 2.0, 3.0, 4.0 ]

var bool = ( out === y );
// returns true

The function accepts the following additional arguments:

• offsetView: starting index (in bytes) for view.
• offsetOut: starting index for out.

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

var Float64Array = require( '@stdlib/array-float64' );
var DataView = require( '@stdlib/array-dataview' );

var x = new Float64Array( [ 1.0, 2.0, 3.0, 4.0 ] );
var view = new DataView( x.buffer );

var y = new Float64Array( x.length*2 );
var out = readDataView.ndarray( x.length, view, -8, 24, y, 2, 1, true );
// e.g., returns <Float64Array>[ 0.0, 4.0, 0.0, 3.0, 0.0, 2.0, 0.0, 1.0 ]

var bool = ( out === y );
// returns true

Examples

var DataView = require( '@stdlib/array-dataview' );
var typedarray = require( '@stdlib/array-typed' );
var bytesPerElement = require( '@stdlib/ndarray-base-bytes-per-element' );
var discreteUniform = require( '@stdlib/random-array-discrete-uniform' );
var IS_LITTLE_ENDIAN = require( '@stdlib/assert-is-little-endian' );
var logEach = require( '@stdlib/console-log-each' );
var readDataView = require( '@stdlib/strided-base-read-dataview' );

// Specify the array data type:
var dtype = 'float64';

// Resolve the number of bytes per element:
var nbytes = bytesPerElement( dtype );

// Generate an array of random numbers:
var x = discreteUniform( 10, 0, 100, {
    'dtype': dtype
});

// Create a DataView:
var view = new DataView( x.buffer );

// Create an output array:
var out = typedarray( x.length, dtype );

// Read elements from the DataView according to host byte order:
readDataView( out.length, view, nbytes, out, 1, IS_LITTLE_ENDIAN );

// Print the results:
logEach( '%d -> %d', x, out );

// Read elements from the DataView according to the opposite byte order:
readDataView( out.length, view, nbytes, out, 1, !IS_LITTLE_ENDIAN );

// Print the results:
logEach( '%d -> %d', x, out );

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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.

Community

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License

See LICENSE.

Copyright

Copyright © 2016-2025. The Stdlib Authors.