# ssorthp
> Sort a single-precision floating-point strided array using heapsort.
## Usage
```javascript
var ssorthp = require( '@stdlib/blas/ext/base/ssorthp' );
```
#### ssorthp( N, order, x, stride )
Sorts a single-precision floating-point strided array using heapsort.
```javascript
var Float32Array = require( '@stdlib/array/float32' );
var x = new Float32Array( [ 1.0, -2.0, 3.0, -4.0 ] );
ssorthp( 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 [`Float32Array`][@stdlib/array/float32].
- **stride**: index increment.
The `N` and stride parameters determine which elements in the strided arrays are accessed at runtime. For example, to sort every other element
```javascript
var Float32Array = require( '@stdlib/array/float32' );
var x = new Float32Array( [ 1.0, -2.0, 3.0, -4.0 ] );
ssorthp( 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`][mdn-typed-array] views.
```javascript
var Float32Array = require( '@stdlib/array/float32' );
// Initial array...
var x0 = new Float32Array( [ 1.0, 2.0, 3.0, 4.0 ] );
// Create an offset view...
var x1 = new Float32Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 );
// Sort every other element...
ssorthp( 2, -1.0, x1, 2 );
// x0 => [ 1.0, 4.0, 3.0, 2.0 ]
```
#### ssorthp.ndarray( N, order, x, stride, offset )
Sorts a single-precision floating-point strided array using heapsort and alternative indexing semantics.
```javascript
var Float32Array = require( '@stdlib/array/float32' );
var x = new Float32Array( [ 1.0, -2.0, 3.0, -4.0 ] );
ssorthp.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`][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 of the strided array
```javascript
var Float32Array = require( '@stdlib/array/float32' );
var x = new Float32Array( [ 1.0, -2.0, 3.0, -4.0, 5.0, -6.0 ] );
ssorthp.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 the strided array 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 complexity `O(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 **in-place** (i.e., the input strided array is **mutated**).
## Examples
```javascript
var discreteUniform = require( '@stdlib/random/base/discrete-uniform' ).factory;
var filledarrayBy = require( '@stdlib/array/filled-by' );
var ssorthp = require( '@stdlib/blas/ext/base/ssorthp' );
var rand = discreteUniform( -100, 100 );
var x = filledarrayBy( 10, 'float32', rand );
console.log( x );
ssorthp( 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][@williams:1964a].
- 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][@floyd:1964a].
[@stdlib/array/float32]: https://www.npmjs.com/package/@stdlib/array-float32
[mdn-typed-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray
[@williams:1964a]: https://doi.org/10.1145/512274.512284
[@floyd:1964a]: https://doi.org/10.1145/355588.365103
[@stdlib/blas/ext/base/dsorthp]: https://github.com/stdlib-js/blas/tree/main/ext/base/dsorthp
[@stdlib/blas/ext/base/gsorthp]: https://github.com/stdlib-js/blas/tree/main/ext/base/gsorthp
[@stdlib/blas/ext/base/ssort2hp]: https://github.com/stdlib-js/blas/tree/main/ext/base/ssort2hp