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README.md

gsort

Sort a strided array.

Usage

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

gsort( N, order, x, strideX )

Sorts a strided array.

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

gsort( x.length, 1.0, x, 1 );
// x => [ -4.0, -2.0, 1.0, 3.0 ]

The function has the following parameters:

  • N: number of indexed elements.
  • order: sort order. If order < 0.0, the input strided array is sorted in decreasing order. If order > 0.0, the input strided array is sorted in increasing order. If order == 0.0, the input strided array is left unchanged.
  • x: input Array or typed array.
  • strideX: stride length.

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

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

gsort( 2, -1.0, x, 2 );
// x => [ 3.0, -2.0, 1.0, -4.0 ]

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 ] );

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

// Sort every other element...
gsort( 2, -1.0, x1, 2 );
// x0 => <Float64Array>[ 1.0, 4.0, 3.0, 2.0 ]

gsort.ndarray( N, order, x, strideX, offsetX )

Sorts a strided array using alternative indexing semantics.

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

gsort.ndarray( x.length, 1.0, x, 1, 0 );
// x => [ -4.0, -2.0, 1.0, 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:

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

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

Notes

  • If N <= 0 or order == 0.0, both functions return x unchanged.
  • The algorithm distinguishes between -0 and +0. When sorted in increasing order, -0 is sorted before +0. When sorted in decreasing order, -0 is sorted after +0.
  • The algorithm sorts NaN values to the end. When sorted in increasing order, NaN values are sorted last. When sorted in decreasing order, NaN values are sorted first.
  • The input strided array is sorted in-place (i.e., the input strided array is mutated).

Examples

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

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

gsort( x.length, -1.0, x, -1 );
console.log( x );