Reverse a strided array in-place.
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> Reverse a strided array in-place.
``bash`
npm install @stdlib/blas-ext-base-grev
`javascript`
var grev = require( '@stdlib/blas-ext-base-grev' );
#### grev( N, x, strideX )
Reverses a strided array in-place.
`javascript
var x = [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ];
grev( x.length, x, 1 );
// x => [ -3.0, -1.0, 0.0, 4.0, -5.0, 3.0, 1.0, -2.0 ]
`
The function has the following parameters:
- N: number of indexed elements.
- x: input array.
- strideX: stride length.
The N and stride parameters determine which elements in the strided array are accessed at runtime. For example, to reverse every other element:
`javascript
var x = [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ];
grev( 4, x, 2 );
// x => [ -1.0, 1.0, 4.0, -5.0, 3.0, 0.0, -2.0, -3.0 ]
`
Note that indexing is relative to the first index. To introduce an offset, use [typed array][mdn-typed-array] views.
`javascript
var Float64Array = require( '@stdlib/array-float64' );
// 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
// Reverse every other element...
grev( 3, x1, 2 );
// x0 =>
`
#### grev.ndarray( N, x, strideX, offsetX )
Reverses a strided array in-place using alternative indexing semantics.
`javascript
var x = [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ];
grev.ndarray( x.length, x, 1, 0 );
// x => [ -3.0, -1.0, 0.0, 4.0, -5.0, 3.0, 1.0, -2.0 ]
`
The function has the following additional parameters:
- offsetX: starting index.
While [typed array][mdn-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:
`javascript
var x = [ 1.0, -2.0, 3.0, -4.0, 5.0, -6.0 ];
grev.ndarray( 3, x, 1, x.length-3 );
// x => [ 1.0, -2.0, 3.0, -6.0, 5.0, -4.0 ]
`
- If N <= 0, both functions return x unchanged.@stdlib/array-complex64
- Both functions support array-like objects having getter and setter accessors for array element access (e.g., [][@stdlib/array/complex64]).O(1)
- Where possible, one should "reverse" a strided array by negating its stride, which is an operation, in contrast to performing an in-place reversal, which is O(N). However, in certain circumstances, this is not tenable, particularly when interfacing with libraries which assume and/or expect a specific memory layout (e.g., strided array elements arranged in memory in ascending order). In general, when working with strided arrays, only perform an in-place reversal when strictly necessary.drev
- Depending on the environment, the typed versions ([][@stdlib/blas/ext/base/drev], [srev][@stdlib/blas/ext/base/srev], etc.) are likely to be significantly more performant.
`javascript
var discreteUniform = require( '@stdlib/random-base-discrete-uniform' ).factory;
var Float64Array = require( '@stdlib/array-float64' );
var gfillBy = require( '@stdlib/blas-ext-base-gfill-by' );
var grev = require( '@stdlib/blas-ext-base-grev' );
var x = gfillBy( 10, new Float64Array( 10 ), 1, discreteUniform( -100, 100 ) );
console.log( x );
grev( x.length, x, 1 );
console.log( x );
`
*
- [@stdlib/blas-ext/base/drev][@stdlib/blas/ext/base/drev]: reverse a double-precision floating-point strided array in-place.
- [@stdlib/blas-ext/base/srev][@stdlib/blas/ext/base/srev]: reverse a single-precision floating-point strided array in-place.
*
This package is part of [stdlib][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][stdlib], see the main project [repository][stdlib].
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