feat: add stats/strided/dnancount

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

@@ -0,0 +1,290 @@
+<!--
+
+@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.
+
+-->
+
+# dnancount
+
+> Calculate the number of non-`NaN` elements in a double-precision floating-point strided array.
+
+<section class="intro">
+
+</section>
+
+<!-- /.intro -->
+
+<section class="usage">
+
+## Usage
+
+```javascript
+var dnancount = require( '@stdlib/stats/strided/dnancount' );
+```
+
+#### dnancount( N, x, strideX )
+
+Computes the number of non-`NaN` elements in a double-precision floating-point strided array.
+
+```javascript
+var Float64Array = require( '@stdlib/array/float64' );
+
+var x = new Float64Array( [ 1.0, -2.0, NaN, 2.0 ] );
+
+var v = dnancount( x.length, x, 1 );
+// returns 3
+```
+
+The function has the following parameters:
+
+-   **N**: number of indexed elements.
+-   **x**: input [`Float64Array`][@stdlib/array/float64].
+-   **strideX**: stride length for `x`.
+
+The `N` and stride parameters determine which elements in the strided array are accessed at runtime. For example, to count every other element in `x`,
+
+```javascript
+var Float64Array = require( '@stdlib/array/float64' );
+
+var x = new Float64Array( [ 1.0, 2.0, NaN, -2.0, 4.0, 3.0, NaN, NaN ] );
+
+var v = dnancount( 4, x, 2 );
+// returns 2
+```
+
+Note that indexing is relative to the first index. To introduce an offset, use [`typed array`][mdn-typed-array] views.
+
+<!-- eslint-disable stdlib/capitalized-comments -->
+
+```javascript
+var Float64Array = require( '@stdlib/array/float64' );
+
+var x0 = new Float64Array( [ 2.0, 1.0, NaN, -2.0, 3.0, 4.0, NaN, NaN ] );
+var x1 = new Float64Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element
+
+var v = dnancount( 4, x1, 2 );
+// returns 3
+```
+
+#### dnancount.ndarray( N, x, strideX, offsetX )
+
+Computes the number of non-`NaN` elements in a double-precision floating-point strided array using alternative indexing semantics.
+
+```javascript
+var Float64Array = require( '@stdlib/array/float64' );
+
+var x = new Float64Array( [ 2.0, 1.0, -2.0, -2.0, 3.0, 4.0, NaN, NaN ] );
+
+var v = dnancount.ndarray( 4, x, 2, 1 );
+// returns 3
+```
+
+The function has the following additional parameter:
+
+-   **offsetX**: starting index for `x`.
+
+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 count every other element in `x` starting from the second element,
+
+```javascript
+var Float64Array = require( '@stdlib/array/float64' );
+
+var x = new Float64Array( [ 2.0, 1.0, NaN, -2.0, 3.0, 4.0, NaN, NaN ] );
+
+var v = dnancount.ndarray( 4, x, 2, 1 );
+// returns 3
+```
+
+</section>
+
+<!-- /.usage -->
+
+<section class="notes">
+
+## Notes
+
+-   If `N <= 0`, both functions return `0`.
+
+</section>
+
+<!-- /.notes -->
+
+<section class="examples">
+
+## Examples
+
+<!-- eslint no-undef: "error" -->
+
+```javascript
+var uniform = require( '@stdlib/random/base/uniform' );
+var filledarrayBy = require( '@stdlib/array/filled-by' );
+var bernoulli = require( '@stdlib/random/base/bernoulli' );
+var dnancount = require( '@stdlib/stats/strided/dnancount' );
+
+function rand() {
+    if ( bernoulli( 0.8 ) < 1 ) {
+        return NaN;
+    }
+    return uniform( -50.0, 50.0 );
+}
+
+var x = filledarrayBy( 10, 'float64', rand );
+console.log( x );
+
+var v = dnancount( x.length, x, 1 );
+console.log( v );
+```
+
+</section>
+
+<!-- /.examples -->
+
+* * *
+
+<section class="c">
+
+## C APIs
+
+<section class="intro">
+
+</section>
+
+<!-- /.intro -->
+
+<section class="usage">
+
+### Usage
+
+```c
+#include "stdlib/stats/strided/dnancount.h"
+```
+
+#### stdlib_strided_dnancount( N, \*X, strideX )
+
+Computes the number of non-`NaN` elements in a double-precision floating-point strided array.
+
+```c
+const double x[] = { 1.0, 2.0, NaN, 4.0, 5.0, 6.0, NaN, 8.0 };
+
+int v = stdlib_strided_dnancount( 4, x, 2 );
+// returns 2
+```
+
+The function accepts the following arguments:
+
+-   **N**: `[in] CBLAS_INT` number of indexed elements.
+-   **X**: `[in] double*` input array.
+-   **strideX**: `[in] CBLAS_INT` stride length for `X`.
+
+```c
+CBLAS_INT stdlib_strided_dnancount( const CBLAS_INT N, const double *X, const CBLAS_INT strideX );
+```
+
+#### stdlib_strided_dnancount_ndarray( N, \*X, strideX, offsetX )
+
+Computes the number of non-`NaN` elements in a double-precision floating-point strided array using alternative indexing semantics.
+
+```c
+const double x[] = { 2.0, 1.0, NaN, -2.0, 3.0, 4.0, NaN, NaN };
+
+int v = stdlib_strided_dnancount_ndarray( 4, x, 2, 1 );
+// returns 3
+```
+
+The function accepts the following arguments:
+
+-   **N**: `[in] CBLAS_INT` number of indexed elements.
+-   **X**: `[in] double*` input array.
+-   **strideX**: `[in] CBLAS_INT` stride length for `X`.
+-   **offsetX**: `[in] CBLAS_INT` starting index for `X`.
+
+```c
+CBLAS_INT stdlib_strided_dnancount_ndarray( const CBLAS_INT N, const double *X, const CBLAS_INT strideX, const CBLAS_INT offsetX );
+```
+
+</section>
+
+<!-- /.usage -->
+
+<section class="notes">
+
+### Notes
+
+-   If `N <= 0`, both functions return `0`.
+
+</section>
+
+<!-- /.notes -->
+
+<section class="examples">
+
+### Examples
+
+```c
+#include "stdlib/stats/strided/dnancount.h"
+#include <stdint.h>
+#include <stdio.h>
+
+int main( void ) {
+    // Create a strided array:
+    const double x[] = { 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 0.0/0.0, 0.0/0.0 };
+
+    // Specify the number of elements:
+    const int N = 5;
+
+    // Specify the stride length:
+    const int strideX = 2;
+
+    // Compute the number of non-NaN elements:
+    int v = stdlib_strided_dnancount( N, x, strideX );
+
+    // Print the result:
+    printf( "count: %d\n", v );
+}
+```
+
+</section>
+
+<!-- /.examples -->
+
+</section>
+
+<!-- /.c -->
+
+<!-- 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">
+
+[@stdlib/array/float64]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/array/float64
+
+[mdn-typed-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray
+
+<!-- <related-links> -->
+
+
+<!-- </related-links> -->
+
+</section>
+
+<!-- /.links -->