time-to-botec

README.md (5877B)

---

 <!--
 
 @license Apache-2.0
 
 Copyright (c) 2020 The Stdlib Authors.
 
 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
 You may obtain a copy of the License at
 
    http://www.apache.org/licenses/LICENSE-2.0
 
 Unless required by applicable law or agreed to in writing, software
 distributed under the License is distributed on an "AS IS" BASIS,
 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 See the License for the specific language governing permissions and
 limitations under the License.
 
 -->
 
 # gsorthp
 
 > Sort a strided array using heapsort.
 
 <section class="usage">
 
 ## Usage
 
 ```javascript
 var gsorthp = require( '@stdlib/blas/ext/base/gsorthp' );
 ```
 
 #### gsorthp( N, order, x, stride )
 
 Sorts a strided array `x` using heapsort.
 
 ```javascript
 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. 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`][mdn-array] or [`typed array`][mdn-typed-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
 
 ```javascript
 var floor = require( '@stdlib/math/base/special/floor' );
 
 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`][mdn-typed-array] views.
 
 ```javascript
 var Float64Array = require( '@stdlib/array/float64' );
 var floor = require( '@stdlib/math/base/special/floor' );
 
 // 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.
 
 ```javascript
 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`][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 `x`
 
 ```javascript
 var x = [ 1.0, -2.0, 3.0, -4.0, 5.0, -6.0 ];
 
 gsorthp.ndarray( 3, 1.0, x, 1, x.length-3 );
 // x => [ 1.0, -2.0, 3.0, -6.0, -4.0, 5.0 ]
 ```
 
 </section>
 
 <!-- /.usage -->
 
 <section class="notes">
 
 ## 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 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**).
 -   Depending on the environment, the typed versions ([`dsorthp`][@stdlib/blas/ext/base/dsorthp], [`ssorthp`][@stdlib/blas/ext/base/ssorthp], etc.) are likely to be significantly more performant.
 
 </section>
 
 <!-- /.notes -->
 
 <section class="examples">
 
 ## Examples
 
 <!-- eslint no-undef: "error" -->
 
 ```javascript
 var round = require( '@stdlib/math/base/special/round' );
 var randu = require( '@stdlib/random/base/randu' );
 var Float64Array = require( '@stdlib/array/float64' );
 var gsorthp = require( '@stdlib/blas/ext/base/gsorthp' );
 
 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 );
 ```
 
 </section>
 
 <!-- /.examples -->
 
 * * *
 
 <section class="references">
 
 ## 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].
 
 </section>
 
 <!-- /.references -->
 
 <section class="links">
 
 [mdn-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array
 
 [mdn-typed-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray
 
 [@stdlib/blas/ext/base/dsorthp]: https://www.npmjs.com/package/@stdlib/blas/tree/main/ext/base/dsorthp
 
 [@stdlib/blas/ext/base/ssorthp]: https://www.npmjs.com/package/@stdlib/blas/tree/main/ext/base/ssorthp
 
 [@williams:1964a]: https://doi.org/10.1145/512274.512284
 
 [@floyd:1964a]: https://doi.org/10.1145/355588.365103
 
 </section>
 
 <!-- /.links -->