npm package: @stdlib/blas-ext-base-ndarray-gfind-index
Description: Return the index of the first element in a one-dimensional ndarray which passes a test implemented by a predicate function.
Author: The Stdlib Authors
Latest version: 0.1.1

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# gfindIndex

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> Return the index of the first element in a one-dimensional ndarray which passes a test implemented by a predicate function.

<section class="intro">

</section>

<!-- /.intro -->

<section class="installation">

## Installation

```bash
npm install @stdlib/blas-ext-base-ndarray-gfind-index
```

</section>

<section class="usage">

## Usage

```javascript
var gfindIndex = require( '@stdlib/blas-ext-base-ndarray-gfind-index' );
```

#### gfindIndex( arrays, clbk\[, thisArg] )

Returns the index of the first element in a one-dimensional ndarray which passes a test implemented by a predicate function.

```javascript
var ndarray = require( '@stdlib/ndarray-base-ctor' );

function isEven( v ) {
    return v % 2.0 === 0.0;
}

var xbuf = [ 1.0, 3.0, 4.0, 2.0 ];
var x = new ndarray( 'generic', xbuf, [ 4 ], [ 1 ], 0, 'row-major' );

var idx = gfindIndex( [ x ], isEven );
// returns 2
```

If no element passes a test implemented by a predicate function, the function returns `-1`.

```javascript
var ndarray = require( '@stdlib/ndarray-base-ctor' );

function isEven( v ) {
    return v % 2.0 === 0.0;
}

var xbuf = [ 1.0, 3.0, 5.0, 7.0 ];
var x = new ndarray( 'generic', xbuf, [ 4 ], [ 1 ], 0, 'row-major' );

var idx = gfindIndex( [ x ], isEven );
// returns -1
```

The function has the following parameters:

-   **arrays**: array-like object containing a one-dimensional input ndarray.
-   **clbk**: callback function.
-   **thisArg**: callback execution context (_optional_).

The callback function is provided the following arguments:

-   **value**: current array element.
-   **idx**: current array element index.
-   **array**: the input ndarray.

To set the callback execution context, provide a `thisArg`.

```javascript
var ndarray = require( '@stdlib/ndarray-base-ctor' );

function isEven( v ) {
    this.count += 1;
    return v % 2.0 === 0.0;
}

var xbuf = [ 1.0, 3.0, 4.0, 2.0 ];
var x = new ndarray( 'generic', xbuf, [ 4 ], [ 1 ], 0, 'row-major' );
var ctx = {
    'count': 0
};

var v = gfindIndex( [ x ], isEven, ctx );
// returns 2

var count = ctx.count;
// returns 3
```

</section>

<!-- /.usage -->

<section class="notes">

## Notes

-   If provided an empty one-dimensional ndarray, the function returns `-1`.

</section>

<!-- /.notes -->

<section class="examples">

## Examples

<!-- eslint no-undef: "error" -->

```javascript
var discreteUniform = require( '@stdlib/random-array-discrete-uniform' );
var ndarray = require( '@stdlib/ndarray-base-ctor' );
var ndarray2array = require( '@stdlib/ndarray-to-array' );
var gfindIndex = require( '@stdlib/blas-ext-base-ndarray-gfind-index' );

function isEven( v ) {
    return v % 2.0 === 0.0;
}

var xbuf = discreteUniform( 10, -100, 100, {
    'dtype': 'generic'
});
var x = new ndarray( 'generic', xbuf, [ xbuf.length ], [ 1 ], 0, 'row-major' );
console.log( ndarray2array( x ) );

var idx = gfindIndex( [ x ], isEven );
console.log( idx );
```

</section>

<!-- /.examples -->

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<section class="related">

</section>

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<section class="main-repo" >

* * *

## Notice

This package is part of [stdlib][stdlib], a standard library for JavaScript and Node.js, with an emphasis on numerical and scientific computing. The library provides a collection of robust, high performance libraries for mathematics, statistics, streams, utilities, and more.

For more information on the project, filing bug reports and feature requests, and guidance on how to develop [stdlib][stdlib], see the main project [repository][stdlib].

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---

## License

See [LICENSE][stdlib-license].


## Copyright

Copyright &copy; 2016-2026. The Stdlib [Authors][stdlib-authors].

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