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gsorthp
Sort a strided array using heapsort.
Installation
npm install @stdlib/blasextbasegsorthp
Usage
var gsorthp = require( '@stdlib/blasextbasegsorthp' );
gsorthp( N, order, x, stride )
Sorts a strided array x
using heapsort.
var x = [ 1.0, 2.0, 3.0, 4.0 ];
gsorthp( 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. Iforder > 0.0
, the input strided array is sorted in increasing order. Iforder == 0.0
, the input strided array is left unchanged. 
x: input
Array
ortyped array
.  stride: index increment.
The N
and stride
parameters determine which elements in x
are accessed at runtime. For example, to sort every other element
var floor = require( '@stdlib/mathbasespecialfloor' );
var x = [ 1.0, 2.0, 3.0, 4.0 ];
var N = floor( x.length / 2 );
gsorthp( N, 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/arrayfloat64' );
var floor = require( '@stdlib/mathbasespecialfloor' );
// 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
var N = floor( x0.length/2 );
// Sort every other element...
gsorthp( N, 1.0, x1, 2 );
// x0 => <Float64Array>[ 1.0, 4.0, 3.0, 2.0 ]
gsorthp.ndarray( N, order, x, stride, offset )
Sorts a strided array x
using heapsort and alternative indexing semantics.
var x = [ 1.0, 2.0, 3.0, 4.0 ];
gsorthp.ndarray( x.length, 1.0, x, 1, 0 );
// x => [ 4.0, 2.0, 1.0, 3.0 ]
The function has the following additional parameters:
 offset: 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 x
var x = [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ];
gsorthp.ndarray( 3, 1.0, x, 1, x.length3 );
// x => [ 1.0, 2.0, 3.0, 6.0, 4.0, 5.0 ]
Notes
 If
N <= 0
ororder == 0.0
, both functions returnx
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 algorithm has space complexity
O(1)
and time complexityO(N log2 N)
.  The algorithm is unstable, meaning that the algorithm may change the order of strided array elements which are equal or equivalent (e.g.,
NaN
values).  The input strided array is sorted inplace (i.e., the input strided array is mutated).
 Depending on the environment, the typed versions (
dsorthp
,ssorthp
, etc.) are likely to be significantly more performant.
Examples
var round = require( '@stdlib/mathbasespecialround' );
var randu = require( '@stdlib/randombaserandu' );
var Float64Array = require( '@stdlib/arrayfloat64' );
var gsorthp = require( '@stdlib/blasextbasegsorthp' );
var rand;
var sign;
var x;
var i;
x = new Float64Array( 10 );
for ( i = 0; i < x.length; i++ ) {
rand = round( randu()*100.0 );
sign = randu();
if ( sign < 0.5 ) {
sign = 1.0;
} else {
sign = 1.0;
}
x[ i ] = sign * rand;
}
console.log( x );
gsorthp( x.length, 1.0, x, 1 );
console.log( x );
References
 Williams, John William Joseph. 1964. "Algorithm 232: Heapsort." Communications of the ACM 7 (6). New York, NY, USA: Association for Computing Machinery: 347–49. doi:10.1145/512274.512284.
 Floyd, Robert W. 1964. "Algorithm 245: Treesort." Communications of the ACM 7 (12). New York, NY, USA: Association for Computing Machinery: 701. doi:10.1145/355588.365103.
See Also

@stdlib/blasext/base/dsorthp
: sort a doubleprecision floatingpoint strided array using heapsort. 
@stdlib/blasext/base/gsort2hp
: simultaneously sort two strided arrays based on the sort order of the first array using heapsort. 
@stdlib/blasext/base/ssorthp
: sort a singleprecision floatingpoint strided array using heapsort.
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
License
See LICENSE.
Copyright
Copyright © 20162024. The Stdlib Authors.