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# znancount

> Calculate the number of non-`NaN` elements in a double-precision complex floating-point strided array.

<section class="intro">

</section>

<!-- /.intro -->

<section class="usage">

## Usage

```javascript
var znancount = require( '@stdlib/blas/ext/base/znancount' );
```

#### znancount( N, x, strideX )

Computes the number of non-`NaN` elements in a double-precision complex floating-point strided array.

```javascript
var Complex128Array = require( '@stdlib/array/complex128' );

var x = new Complex128Array( [ 1.0, -2.0, NaN, 2.0 ] );

var v = znancount( x.length, x, 1 );
// returns 1
```

The function has the following parameters:

-   **N**: number of indexed elements.
-   **x**: input [`Complex128Array`][@stdlib/array/complex128].
-   **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 Complex128Array = require( '@stdlib/array/complex128' );

var x = new Complex128Array( [ 1.0, 2.0, NaN, -2.0, 4.0, 3.0, NaN, NaN ] );

var v = znancount( 2, 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 Complex128Array = require( '@stdlib/array/complex128' );

var x0 = new Complex128Array( [ 2.0, 1.0, NaN, -2.0, 3.0, 4.0, NaN, NaN ] );
var x1 = new Complex128Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element

var v = znancount( 2, x1, 2 );
// returns 0
```

#### znancount.ndarray( N, x, strideX, offsetX )

Computes the number of non-`NaN` elements in a double-precision complex floating-point strided array using alternative indexing semantics.

```javascript
var Complex128Array = require( '@stdlib/array/complex128' );

var x = new Complex128Array( [ 2.0, 1.0, -2.0, -2.0, 3.0, 4.0, NaN, NaN ] );

var v = znancount.ndarray( 4, x, 1, 0 );
// 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 Complex128Array = require( '@stdlib/array/complex128' );

var x = new Complex128Array( [ 2.0, 1.0, NaN, -2.0, 3.0, 4.0, NaN, NaN ] );

var v = znancount.ndarray( 2, x, 2, 1 );
// returns 0
```

</section>

<!-- /.usage -->

<section class="notes">

## Notes

-   If `N <= 0`, both functions return `0`.
-   An element is considered `NaN` if either its real or imaginary component is `NaN`.

</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 Complex128Array = require( '@stdlib/array/complex128' );
var znancount = require( '@stdlib/blas/ext/base/znancount' );

function rand() {
    if ( bernoulli( 0.8 ) < 1 ) {
        return NaN;
    }
    return uniform( -50.0, 50.0 );
}

var xbuf = filledarrayBy( 10, 'float64', rand );
console.log( xbuf );

var x = new Complex128Array( xbuf );
var v = znancount( x.length, x, 1 );
console.log( v );
```

</section>

<!-- /.examples -->

<!-- C interface documentation. -->

* * *

<section class="c">

## C APIs

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<section class="intro">

</section>

<!-- /.intro -->

<!-- C usage documentation. -->

<section class="usage">

### Usage

```c
#include "stdlib/blas/ext/base/znancount.h"
```

#### stdlib_strided_znancount( N, \*X, strideX )

Computes the number of non-`NaN` elements in a double-precision complex floating-point strided array.

```c
#include "stdlib/complex/float64/ctor.h"

const stdlib_complex128_t x[] = {
    stdlib_complex128( 2.0, 1.0 ),
    stdlib_complex128( NaN, -2.0 ),
    stdlib_complex128( 3.0, 4.0 ),
    stdlib_complex128( NaN, NaN )
};

int v = stdlib_strided_znancount( 4, x, 1 );
// returns 2
```

The function accepts the following arguments:

-   **N**: `[in] CBLAS_INT` number of indexed elements.
-   **X**: `[in] stdlib_complex128_t*` input array.
-   **strideX**: `[in] CBLAS_INT` stride length for `X`.

```c
CBLAS_INT stdlib_strided_znancount( const CBLAS_INT N, const stdlib_complex128_t *X, const CBLAS_INT strideX );
```

#### stdlib_strided_znancount_ndarray( N, \*X, strideX, offsetX )

Computes the number of non-`NaN` elements in a double-precision complex floating-point strided array using alternative indexing semantics.

```c
#include "stdlib/complex/float64/ctor.h"

const stdlib_complex128_t x[] = {
    stdlib_complex128( 2.0, 1.0 ),
    stdlib_complex128( NaN, -2.0 ),
    stdlib_complex128( 3.0, 4.0 ),
    stdlib_complex128( NaN, NaN )
};

int v = stdlib_strided_znancount_ndarray( 4, x, 1, 0 );
// returns 2
```

The function accepts the following arguments:

-   **N**: `[in] CBLAS_INT` number of indexed elements.
-   **X**: `[in] stdlib_complex128_t*` input array.
-   **strideX**: `[in] CBLAS_INT` stride length for `X`.
-   **offsetX**: `[in] CBLAS_INT` starting index for `X`.

```c
CBLAS_INT stdlib_strided_znancount_ndarray( const CBLAS_INT N, const stdlib_complex128_t *X, const CBLAS_INT strideX, const CBLAS_INT offsetX );
```

</section>

<!-- /.usage -->

<!-- C API usage notes. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->

<section class="notes">

### Notes

-   If `N <= 0`, both functions return `0`.
-   An element is considered `NaN` if either its real or imaginary component is `NaN`.

</section>

<!-- /.notes -->

<!-- C API usage examples. -->

<section class="examples">

### Examples

```c
#include "stdlib/blas/ext/base/znancount.h"
#include "stdlib/complex/float64/ctor.h"
#include <stdio.h>

int main( void ) {
    // Create a strided array:
    const stdlib_complex128_t x[] = {
        stdlib_complex128( 1.0, 2.0 ),
        stdlib_complex128( 3.0, 4.0 ),
        stdlib_complex128( 0.0/0.0, 5.0 ), // NaN
        stdlib_complex128( 6.0, 0.0/0.0 ), // NaN
        stdlib_complex128( 7.0, 8.0 )
    };

    // Specify the number of elements:
    const int N = 5;

    // Specify the stride length:
    const int strideX = 1;

    // Compute the number of non-NaN elements:
    int v = stdlib_strided_znancount( 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/complex128]: https://www.npmjs.com/package/@stdlib/array-complex128

[mdn-typed-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray

<!-- <related-links> -->

<!-- </related-links> -->

</section>

<!-- /.links -->
