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gcircshift

Circularly shift the elements of a strided array by a specified number of positions.

Usage

var gcircshift = require( '@stdlib/blas/ext/base/gcircshift' );

gcircshift( N, k, x, strideX )

Circularly shifts the elements of a strided array by a specified number of positions.

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

gcircshift( x.length, 2, x, 1 );
// x => [ 4.0, 5.0, 1.0, 2.0, 3.0 ]

The function has the following parameters:

  • N: number of indexed elements.
  • k: number of positions to shift.
  • 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 circularly shift every other element:

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

gcircshift( 4, 1, x, 2 );
// x => [ 4.0, 0.0, 1.0, 0.0, 2.0, 0.0, 3.0, 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' );

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

// Create an offset view...
var x1 = new Float64Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element

// Circularly shift elements in the view:
gcircshift( 5, 2, x1, 1 );
// x0 => <Float64Array>[ 0.0, 4.0, 5.0, 1.0, 2.0, 3.0 ]

gcircshift.ndarray( N, k, x, strideX, offsetX )

Circularly shifts the elements of a strided array by a specified number of positions using alternative indexing semantics.

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

gcircshift.ndarray( x.length, 2, x, 1, 0 );
// x => [ 4.0, 5.0, 1.0, 2.0, 3.0 ]

The function has the following additional parameters:

  • offsetX: starting index.

While 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 of the strided array:

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

gcircshift.ndarray( 3, 1, x, 1, x.length-3 );
// x => [ 1.0, 2.0, 3.0, 6.0, 4.0, 5.0 ]

Notes

  • If N <= 0, both functions return the strided array unchanged.
  • If k is a multiple of N, both functions return the strided array unchanged.
  • If k > 0, elements are shifted to the right.
  • If k < 0, elements are shifted to the left.
  • Depending on the environment, the typed versions (dcircshift, scircshift, etc.) are likely to be significantly more performant.

Examples

var discreteUniform = require( '@stdlib/random/array/discrete-uniform' );
var gcircshift = require( '@stdlib/blas/ext/base/gcircshift' );

var x = discreteUniform( 10, -100, 100, {
    'dtype': 'generic'
});
console.log( x );

gcircshift( x.length, 3, x, 1 );
console.log( x );