feat: add ndarray/find

lib/node_modules/@stdlib/ndarray/find/README.md

@@ -0,0 +1,339 @@
+<!--
+
+@license Apache-2.0
+
+Copyright (c) 2025 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.
+
+-->
+
+# find
+
+> Return a new [ndarray][@stdlib/ndarray/ctor] containing the first elements which pass a test implemented by a predicate function along one or more [ndarray][@stdlib/ndarray/ctor] dimensions.
+
+<section class="intro">
+
+</section>
+
+<!-- /.intro -->
+
+<section class="usage">
+
+## Usage
+
+<!-- eslint-disable no-redeclare -->
+
+```javascript
+var find = require( '@stdlib/ndarray/find' );
+```
+
+<!-- eslint-enable no-redeclare -->
+
+#### find( x\[, options], predicate\[, thisArg] )
+
+Returns a new [ndarray][@stdlib/ndarray/ctor] containing the first elements which pass a test implemented by a predicate function along one or more [ndarray][@stdlib/ndarray/ctor] dimensions.
+
+<!-- eslint-disable no-invalid-this, max-len -->
+
+```javascript
+var array = require( '@stdlib/ndarray/array' );
+
+function isEven( value ) {
+    return value % 2.0 === 0.0;
+}
+
+// Create an input ndarray:
+var x = array( [ [ [ 1.0, 2.0 ], [ 3.0, 4.0 ] ], [ [ 5.0, 6.0 ], [ 7.0, 8.0 ] ] ] );
+// returns <ndarray>
+
+// Perform reduction:
+var out = find( x, isEven );
+// returns <ndarray>
+
+var v = out.get();
+// returns 2.0
+```
+
+The function accepts the following arguments:
+
+-   **x**: input [ndarray][@stdlib/ndarray/ctor].
+-   **options**: function options _(optional)_.
+-   **predicate**: predicate function.
+-   **thisArg**: predicate function execution context _(optional)_.
+
+The function accepts the following options:
+
+-   **dims**: list of dimensions over which to perform a reduction.
+-   **keepdims**: boolean indicating whether the reduced dimensions should be included in the returned [ndarray][@stdlib/ndarray/ctor] as singleton dimensions. Default: `false`.
+-   **sentinelValue**: value to return when no element passes the test. May be either a scalar value or a zero-dimensional [ndarray][@stdlib/ndarray/ctor].
+
+By default, the function performs reduction over all all elements in a provided [ndarray][@stdlib/ndarray/ctor]. To reduce specific dimensions, set the `dims` option.
+
+```javascript
+var array = require( '@stdlib/ndarray/array' );
+var ndarray2array = require( '@stdlib/ndarray/to-array' );
+
+function isEven( value ) {
+    return value % 2.0 === 0.0;
+}
+
+// Create an input ndarray:
+var x = array( [ [ [ 1.0, 2.0 ], [ 3.0, 4.0 ] ], [ [ 5.0, 6.0 ], [ 7.0, 8.0 ] ] ] );
+// returns <ndarray>
+
+var opts = {
+    'dims': [ 0 ]
+};
+
+// Perform reduction:
+var out = find( x, opts, isEven );
+// returns <ndarray>
+
+var v = ndarray2array( out );
+// returns [ [ NaN, 2.0 ], [ NaN, 4.0 ] ]
+```
+
+By default, the function returns an [ndarray][@stdlib/ndarray/ctor] having a shape matching only the non-reduced dimensions of the input [ndarray][@stdlib/ndarray/ctor] (i.e., the reduced dimensions are dropped). To include the reduced dimensions as singleton dimensions in the output [ndarray][@stdlib/ndarray/ctor], set the `keepdims` option to `true`.
+
+```javascript
+var array = require( '@stdlib/ndarray/array' );
+var ndarray2array = require( '@stdlib/ndarray/to-array' );
+
+function isEven( value ) {
+    return value % 2.0 === 0.0;
+}
+
+// Create an input ndarray:
+var x = array( [ [ [ 1.0, 2.0 ], [ 3.0, 4.0 ] ], [ [ 5.0, 6.0 ], [ 7.0, 8.0 ] ] ] );
+// returns <ndarray>
+
+var opts = {
+    'dims': [ 0 ],
+    'keepdims': true
+};
+
+// Perform reduction:
+var out = find( x, opts, isEven );
+// returns <ndarray>
+
+var v = ndarray2array( out );
+// returns [ [ [ NaN, 2 ], [ NaN, 4 ] ] ]
+```
+
+To specify a custom sentinel value to return when no element passes the test, set the `sentinelValue` option.
+
+```javascript
+var array = require( '@stdlib/ndarray/array' );
+var ndarray2array = require( '@stdlib/ndarray/to-array' );
+
+function isEven( value ) {
+    return value % 2.0 === 0.0;
+}
+
+// Create an input ndarray:
+var x = array( [ [ [ 1.0, 3.0 ], [ 5.0, 7.0 ] ], [ [ 9.0, 11.0 ], [ 13.0, 15.0 ] ] ] );
+// returns <ndarray>
+
+var opts = {
+    'sentinelValue': -999
+};
+
+// Perform reduction:
+var out = find( x, opts, isEven );
+// returns <ndarray>
+
+var v = out.get();
+// returns -999
+```
+
+To set the `predicate` function execution context, provide a `thisArg`.
+
+<!-- eslint-disable no-invalid-this -->
+
+```javascript
+var array = require( '@stdlib/ndarray/array' );
+var ndarray2array = require( '@stdlib/ndarray/to-array' );
+
+function isEven( value ) {
+    this.count += 1;
+    return value % 2.0 === 0.0;
+}
+
+// Create an input ndarray:
+var x = array( [ [ [ 1.0, 2.0 ], [ 3.0, 4.0 ] ], [ [ 5.0, 6.0 ], [ 7.0, 8.0 ] ] ] );
+// returns <ndarray>
+
+var ctx = {
+    'count': 0
+};
+
+// Perform reduction:
+var out = find( x, isEven, ctx );
+// returns <ndarray>
+
+var v = out.get();
+// returns 2.0
+
+var count = ctx.count;
+// returns 2
+```
+
+#### find.assign( x, out\[, options], predicate\[, thisArg] )
+
+Finds the first elements which pass a test implemented by a predicate function along one or more [ndarray][@stdlib/ndarray/ctor] dimensions and assigns results to a provided output [ndarray][@stdlib/ndarray/ctor].
+
+```javascript
+var array = require( '@stdlib/ndarray/array' );
+var empty = require( '@stdlib/ndarray/empty' );
+
+function isEven( value ) {
+    return value % 2.0 === 0.0;
+}
+
+// Create an input ndarray:
+var x = array( [ [ [ 1.0, 2.0 ], [ 3.0, 4.0 ] ], [ [ 5.0, 6.0 ], [ 7.0, 8.0 ] ] ] );
+// returns <ndarray>
+
+// Create an output ndarray:
+var y = empty( [], {
+    'dtype': x.dtype
+});
+
+// Perform reduction:
+var out = find.assign( x, y, isEven );
+// returns <ndarray>
+
+var bool = ( out === y );
+// returns true
+
+var v = y.get();
+// returns 2.0
+```
+
+The function accepts the following arguments:
+
+-   **x**: input [ndarray][@stdlib/ndarray/ctor].
+-   **out**: output [ndarray][@stdlib/ndarray/ctor].
+-   **options**: function options _(optional)_.
+-   **predicate**: predicate function.
+-   **thisArg**: predicate function execution context _(optional)_.
+
+The function accepts the following options:
+
+-   **dims**: list of dimensions over which to perform a reduction.
+-   **sentinelValue**: value to return when no element passes the test. May be either a scalar value or a zero-dimensional [ndarray][@stdlib/ndarray/ctor].
+
+```javascript
+var array = require( '@stdlib/ndarray/array' );
+var empty = require( '@stdlib/ndarray/empty' );
+var ndarray2array = require( '@stdlib/ndarray/to-array' );
+
+function isEven( value ) {
+    return value % 2.0 === 0.0;
+}
+
+// Create an input ndarray:
+var x = array( [ [ [ 1.0, 2.0 ], [ 3.0, 4.0 ] ], [ [ 5.0, 6.0 ], [ 7.0, 8.0 ] ] ] );
+// returns <ndarray>
+
+// Create an output ndarray:
+var y = empty( [ 2, 2 ], {
+    'dtype': x.dtype
+});
+
+var opts = {
+    'dims': [ 0 ]
+};
+
+// Perform reduction:
+var out = find.assign( x, y, opts, isEven );
+
+var bool = ( out === y );
+// returns true
+
+var v = ndarray2array( y );
+// returns [ [ NaN, 2.0 ], [ NaN, 4.0 ] ]
+```
+
+</section>
+
+<!-- /.usage -->
+
+<section class="notes">
+
+## Notes
+
+-   By default, when no `sentinelValue` is provided, the function returns a default sentinel value based on the input [ndarray][@stdlib/ndarray/ctor] [data-type][@stdlib/ndarray/dtypes]:
+
+    -   real-valued floating-point data types: `NaN`.
+    -   complex-valued floating-point data types: `NaN + NaNj`.
+    -   integer data types: maximum value.
+    -   boolean data types: `false`.
+
+-   The `predicate` function is provided the following arguments:
+
+    -   **value**: current array element.
+    -   **indices**: current array element indices.
+    -   **arr**: the input [ndarray][@stdlib/ndarray/ctor].
+
+</section>
+
+<!-- /.notes -->
+
+<section class="examples">
+
+## Examples
+
+<!-- eslint no-undef: "error" -->
+
+```javascript
+var uniform = require( '@stdlib/random/uniform' );
+var isPositive = require( '@stdlib/assert/is-positive-number' ).isPrimitive;
+var ndarray2array = require( '@stdlib/ndarray/to-array' );
+var find = require( '@stdlib/ndarray/find' );
+
+var x = uniform( [ 2, 4, 5 ], -10.0, 10.0, {
+    'dtype': 'float64'
+});
+console.log( ndarray2array( x ) );
+
+var y = find( x, isPositive );
+console.log( y.get() );
+```
+
+</section>
+
+<!-- /.examples -->
+
+<!-- Section for related `stdlib` packages. Do not manually edit this section, as it is automatically populated. -->
+
+<section class="related">
+
+</section>
+
+<!-- /.related -->
+
+<section class="links">
+
+[@stdlib/ndarray/ctor]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/ndarray/ctor
+
+[@stdlib/ndarray/dtypes]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/ndarray/dtypes
+
+<!-- <related-links> -->
+
+<!-- </related-links> -->
+
+</section>
+
+<!-- /.links -->