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gcopy-within

Perform an in-place copy of elements within a strided array.

Usage

var gcopyWithin = require( '@stdlib/blas/ext/base/gcopy-within' );

gcopyWithin( N, target, start, end, x, strideX )

Performs an in-place copy of elements within a strided array.

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

gcopyWithin( x.length, 3, 1, 4, x, 1 );
// x => [ 1.0, 2.0, 3.0, 2.0, 3.0, 4.0 ]

The function has the following parameters:

  • N: number of indexed elements.
  • target: target index.
  • start: source start index.
  • end: source end index (exclusive).
  • x: input array-like object.
  • strideX: stride length.

The N and stride parameters determine which elements in the strided array are accessed at runtime. For example, to copy every other element:

var x = [ 1.0, 0.0, 3.0, 0.0, 5.0, 0.0, 7.0, 0.0 ];

gcopyWithin( 3, 0, 1, 6, x, 2 );
// x => [ 3.0, 0.0, 5.0, 0.0, 7.0, 0.0, 7.0, 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( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0 ] );

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

// Copy within the view...
gcopyWithin( 3, 0, 2, 5, x1, 1 );
// x0 => <Float64Array>[ 1.0, 4.0, 5.0, 6.0, 5.0, 6.0, 7.0, 8.0 ]

gcopyWithin.ndarray( N, target, start, end, x, strideX, offsetX )

Performs an in-place copy of elements within a strided array using alternative indexing semantics.

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

gcopyWithin.ndarray( x.length, 3, 1, 4, x, 1, 0 );
// x => [ 1.0, 2.0, 3.0, 2.0, 3.0, 4.0 ]

The function has the following additional parameters:

  • offsetX: starting index for x.

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 copy elements starting from the second element:

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

gcopyWithin.ndarray( 4, 2, 0, 2, x, 1, 1 );
// x => [ 1.0, 2.0, 3.0, 2.0, 3.0, 6.0 ]

Notes

  • If N <= 0, both functions return the strided array unchanged.
  • If target >= N, both functions return the strided array unchanged.
  • Both functions mutate the provided input strided array.

Examples

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

var x = discreteUniform( 10, 0, 500, {
    'dtype': 'generic'
});
console.log( x );

// Copy the first 3 elements to positions 5, 6, 7:
gcopyWithin( 10, 5, 0, 3, x, 1 );
console.log( x );

// Copy every other element starting from the second element:
gcopyWithin( 5, 0, 1, 9, x, 1 );
console.log( x );