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# gnancount

> Calculate the number of non-`NaN` elements in a strided array.

<section class="intro">

</section>

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<section class="usage">

## Usage

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

#### gnancount( N, x, strideX )

Calculates the number of non-`NaN` elements in a strided array.

```javascript
var x = [ 1.0, -2.0, NaN, 2.0 ];

var v = gnancount( x.length, x, 1 );
// returns 3
```

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`.

The `N` and stride parameters determine which elements in the strided array are accessed at runtime. For example, to calculate the count for every other element in `x`,

```javascript
var x = [ 1.0, 2.0, 2.0, -7.0, -2.0, 3.0, 4.0, 2.0, NaN, NaN ];

var v = gnancount( 5, x, 2 );
// returns 4
```

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, 2.0, -2.0, -2.0, NaN, NaN, 4.0 ] );
var x1 = new Float64Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element

var v = gnancount( 4, x1, 2 );
// returns 3
```

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

Calculates the number of non-`NaN` elements in a strided array using alternative indexing semantics.

```javascript
var x = [ 1.0, -2.0, NaN, 2.0 ];

var v = gnancount.ndarray( x.length, x, 1, 0 );
// returns 3
```

The function has the following additional parameters:

-   **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 calculate the count for every other element in `x` starting from the second element

```javascript
var x = [ 2.0, 1.0, 2.0, -2.0, -2.0, NaN, NaN, 2.0, 3.0, 4.0 ];

var v = gnancount.ndarray( 5, x, 2, 1 );
// returns 4
```

</section>

<!-- /.usage -->

<section class="notes">

## Notes

-   If `N <= 0`, both functions return `0`.
-   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>

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<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 gnancount = require( '@stdlib/blas/ext/base/gnancount' );

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 = gnancount( x.length, x, 1 );
console.log( v );
```

</section>

<!-- /.examples -->

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<section class="related">

</section>

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<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/array/base/accessor]: https://www.npmjs.com/package/@stdlib/array-base-accessor

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</section>

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