feat: add stats/strided/selmax

lib/node_modules/@stdlib/stats/strided/selmax/README.md

@@ -0,0 +1,181 @@
+<!--
+
+@license Apache-2.0
+
+Copyright (c) 2026 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.
+
+-->
+
+# selmax
+
+> Calculate the maximum value of a strided array by selecting elements according to a mask.
+
+<section class="intro">
+
+</section>
+
+<!-- /.intro -->
+
+<section class="usage">
+
+## Usage
+
+```javascript
+var selmax = require( '@stdlib/stats/strided/selmax' );
+```
+
+#### selmax( N, x, strideX, mask, strideMask )
+
+Computes the maximum value of a strided array by selecting elements according to a mask.
+
+```javascript
+var x = [ 1.0, -2.0, 4.0, 2.0 ];
+var mask = [ true, true, false, true ];
+
+var v = selmax( x.length, x, 1, mask, 1 );
+// returns 2.0
+```
+
+The function has the following parameters:
+
+-   **N**: number of indexed elements.
+-   **x**: input [`Array`][mdn-array] or [`typed array`][mdn-typed-array].
+-   **strideX**: stride length for `x`.
+-   **mask**: mask [`Array`][mdn-array] or [`typed array`][mdn-typed-array]. If a `mask` array element is `true`, the corresponding element in `x` is considered valid and **included** in computation. If a `mask` array element is `false`, the corresponding element in `x` is considered invalid/missing and **excluded** from computation.
+-   **strideMask**: stride length for `mask`.
+
+The `N` and stride parameters determine which elements in the strided arrays are accessed at runtime. For example, to compute the maximum value of every other element in `x`,
+
+```javascript
+var x = [ 1.0, 2.0, -7.0, -2.0, 4.0, 3.0, 5.0, 6.0 ];
+var mask = [ true, true, true, true, true, true, false, false ];
+
+var v = selmax( 4, x, 2, mask, 2 );
+// returns 4.0
+```
+
+Note that indexing is relative to the first index. To introduce offsets, use [`typed array`][mdn-typed-array] views.
+
+<!-- eslint-disable stdlib/capitalized-comments, max-len -->
+
+```javascript
+var Float64Array = require( '@stdlib/array/float64' );
+var BooleanArray = require( '@stdlib/array/bool' );
+
+var x0 = new Float64Array( [ 2.0, 1.0, -2.0, -2.0, 3.0, 4.0, 5.0, 6.0 ] );
+var x1 = new Float64Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 );
+
+var mask0 = new BooleanArray( [ true, true, true, true, true, true, false, false ] );
+var mask1 = new BooleanArray( mask0.buffer, mask0.BYTES_PER_ELEMENT*1 );
+
+var v = selmax( 4, x1, 2, mask1, 2 );
+// returns 4.0
+```
+
+#### selmax.ndarray( N, x, strideX, offsetX, mask, strideMask, offsetMask )
+
+Computes the maximum value of a strided array by selecting elements according to a mask and using alternative indexing semantics.
+
+```javascript
+var x = [ 1.0, -2.0, 4.0, 2.0 ];
+var mask = [ true, true, false, true ];
+
+var v = selmax.ndarray( x.length, x, 1, 0, mask, 1, 0 );
+// returns 2.0
+```
+
+The function has the following additional parameters:
+
+-   **offsetX**: starting index for `x`.
+-   **offsetMask**: starting index for `mask`.
+
+While [`typed array`][mdn-typed-array] views mandate a view offset based on the underlying buffer, the offset parameters support indexing semantics based on starting indices. For example, to calculate the maximum value for every other value in `x` starting from the second value
+
+```javascript
+var x = [ 2.0, 1.0, -2.0, -2.0, 3.0, 4.0, 5.0, 6.0 ];
+var mask = [ true, true, true, true, true, true, false, false ];
+
+var v = selmax.ndarray( 4, x, 2, 1, mask, 2, 1 );
+// returns 4.0
+```
+
+</section>
+
+<!-- /.usage -->
+
+<section class="notes">
+
+## Notes
+
+-   If `N <= 0`, both functions return `NaN`.
+-   Both functions support array-like objects having getter and setter accessors for array element access (e.g., [`@stdlib/array/base/accessor`][@stdlib/array/base/accessor]).
+
+</section>
+
+<!-- /.notes -->
+
+<section class="examples">
+
+## Examples
+
+<!-- eslint no-undef: "error" -->
+
+```javascript
+var uniform = require( '@stdlib/random/array/uniform' );
+var bernoulli = require( '@stdlib/random/array/bernoulli' );
+var BooleanArray = require( '@stdlib/array/bool' );
+var selmax = require( '@stdlib/stats/strided/selmax' );
+
+var x = uniform( 10, -50.0, 50.0, {
+    'dtype': 'float64'
+});
+console.log( x );
+
+var mask = new BooleanArray( bernoulli( x.length, 0.8 ) );
+console.log( mask );
+
+var v = selmax( x.length, x, 1, mask, 1 );
+console.log( v );
+```
+
+</section>
+
+<!-- /.examples -->
+
+<!-- Section for related `stdlib` packages. Do not manually edit this section, as it is automatically populated. -->
+
+<section class="related">
+
+</section>
+
+<!-- /.related -->
+
+<!-- Section for all links. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->
+
+<section class="links">
+
+[mdn-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array
+
+[@stdlib/array/base/accessor]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/array/base/accessor
+
+[mdn-typed-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray
+
+<!-- <related-links> -->
+
+<!-- </related-links> -->
+
+</section>
+
+<!-- /.links -->

lib/node_modules/@stdlib/stats/strided/selmax/benchmark/benchmark.js

@@ -0,0 +1,101 @@
+/**
+* @license Apache-2.0
+*
+* Copyright (c) 2026 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.
+*/
+
+'use strict';
+
+// MODULES //
+
+var bench = require( '@stdlib/bench' );
+var isnan = require( '@stdlib/math/base/assert/is-nan' );
+var uniform = require( '@stdlib/random/array/uniform' );
+var bernoulli = require( '@stdlib/random/array/bernoulli' );
+var BooleanArray = require( '@stdlib/array/bool' );
+var pow = require( '@stdlib/math/base/special/pow' );
+var format = require( '@stdlib/string/format' );
+var pkg = require( './../package.json' ).name;
+var selmax = require( './../lib' );
+
+
+// FUNCTIONS //
+
+/**
+* Creates a benchmark function.
+*
+* @private
+* @param {PositiveInteger} len - array length
+* @returns {Function} benchmark function
+*/
+function createBenchmark( len ) {
+	var mask = new BooleanArray( bernoulli( len, 0.8 ) );
+	var x = uniform( len, -10.0, 10.0, {
+		'dtype': 'generic'
+	});
+	return benchmark;
+
+	/**
+	* Benchmark function.
+	*
+	* @private
+	* @param {Benchmark} b - benchmark instance
+	*/
+	function benchmark( b ) {
+		var v;
+		var i;
+
+		b.tic();
+		for ( i = 0; i < b.iterations; i++ ) {
+			v = selmax( x.length, x, 1, mask, 1 );
+			if ( isnan( v ) ) {
+				b.fail( 'should not return NaN' );
+			}
+		}
+		b.toc();
+		if ( isnan( v ) ) {
+			b.fail( 'should not return NaN' );
+		}
+		b.pass( 'benchmark finished' );
+		b.end();
+	}
+}
+
+
+// MAIN //
+
+/**
+* Main execution sequence.
+*
+* @private
+*/
+function main() {
+	var len;
+	var min;
+	var max;
+	var f;
+	var i;
+
+	min = 1; // 10^min
+	max = 6; // 10^max
+
+	for ( i = min; i <= max; i++ ) {
+		len = pow( 10, i );
+		f = createBenchmark( len );
+		bench( format( '%s:len=%d', pkg, len ), f );
+	}
+}
+
+main();

lib/node_modules/@stdlib/stats/strided/selmax/benchmark/benchmark.ndarray.js

@@ -0,0 +1,101 @@
+/**
+* @license Apache-2.0
+*
+* Copyright (c) 2026 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.
+*/
+
+'use strict';
+
+// MODULES //
+
+var bench = require( '@stdlib/bench' );
+var isnan = require( '@stdlib/math/base/assert/is-nan' );
+var uniform = require( '@stdlib/random/array/uniform' );
+var bernoulli = require( '@stdlib/random/array/bernoulli' );
+var BooleanArray = require( '@stdlib/array/bool' );
+var pow = require( '@stdlib/math/base/special/pow' );
+var format = require( '@stdlib/string/format' );
+var pkg = require( './../package.json' ).name;
+var selmax = require( './../lib/ndarray.js' );
+
+
+// FUNCTIONS //
+
+/**
+* Creates a benchmark function.
+*
+* @private
+* @param {PositiveInteger} len - array length
+* @returns {Function} benchmark function
+*/
+function createBenchmark( len ) {
+	var mask = new BooleanArray( bernoulli( len, 0.8 ) );
+	var x = uniform( len, -10.0, 10.0, {
+		'dtype': 'generic'
+	});
+	return benchmark;
+
+	/**
+	* Benchmark function.
+	*
+	* @private
+	* @param {Benchmark} b - benchmark instance
+	*/
+	function benchmark( b ) {
+		var v;
+		var i;
+
+		b.tic();
+		for ( i = 0; i < b.iterations; i++ ) {
+			v = selmax( x.length, x, 1, 0, mask, 1, 0 );
+			if ( isnan( v ) ) {
+				b.fail( 'should not return NaN' );
+			}
+		}
+		b.toc();
+		if ( isnan( v ) ) {
+			b.fail( 'should not return NaN' );
+		}
+		b.pass( 'benchmark finished' );
+		b.end();
+	}
+}
+
+
+// MAIN //
+
+/**
+* Main execution sequence.
+*
+* @private
+*/
+function main() {
+	var len;
+	var min;
+	var max;
+	var f;
+	var i;
+
+	min = 1; // 10^min
+	max = 6; // 10^max
+
+	for ( i = min; i <= max; i++ ) {
+		len = pow( 10, i );
+		f = createBenchmark( len );
+		bench( format( '%s:ndarray:len=%d', pkg, len ), f );
+	}
+}
+
+main();