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# find

> Return the first element in an ndarray which passes a test implemented by a predicate function.

<section class="intro">

</section>

<!-- /.intro -->

<section class="usage">

## Usage

<!-- eslint-disable no-redeclare -->

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

<!-- eslint-enable no-redeclare -->

#### find( arrays, predicate\[, thisArg] )

Returns the first element in an ndarray which passes a test implemented by a predicate function.

<!-- eslint-disable max-len -->

```javascript
var Float64Array = require( '@stdlib/array/float64' );

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

// Create a data buffer:
var xbuf = new Float64Array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, 11.0, 12.0 ] );

// Define the shape of the input array:
var shape = [ 3, 1, 2 ];

// Define the array strides:
var sx = [ 4, 4, 1 ];

// Define the index offset:
var ox = 0;

// Create the input ndarray-like object:
var x = {
    'dtype': 'float64',
    'data': xbuf,
    'shape': shape,
    'strides': sx,
    'offset': ox,
    'order': 'row-major'
};

// Create an ndarray-like object containing a sentinel value:
var sentinelValue = {
    'dtype': 'float64',
    'data': new Float64Array( [ NaN ] ),
    'shape': [],
    'strides': [ 0 ],
    'offset': 0,
    'order': 'row-major'
};

// Perform reduction:
var out = find( [ x, sentinelValue ], isEven );
// returns 2.0
```

The function accepts the following arguments:

-   **arrays**: array-like object containing an input ndarray and a zero-dimensional ndarray containing a sentinel value. The sentinel value is returned when no element in an input ndarray passes a test implemented by the predicate function.
-   **predicate**: predicate function.
-   **thisArg**: predicate function execution context (_optional_).

To set the predicate function execution context, provide a `thisArg`.

<!-- eslint-disable no-invalid-this, max-len -->

```javascript
var Float64Array = require( '@stdlib/array/float64' );

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

// Create a data buffer:
var xbuf = new Float64Array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, 11.0, 12.0 ] );

// Define the shape of the input array:
var shape = [ 3, 1, 2 ];

// Define the array strides:
var sx = [ 4, 4, 1 ];

// Define the index offset:
var ox = 0;

// Create the input ndarray-like object:
var x = {
    'dtype': 'float64',
    'data': xbuf,
    'shape': shape,
    'strides': sx,
    'offset': ox,
    'order': 'row-major'
};

// Create an ndarray-like object containing a sentinel value:
var sentinelValue = {
    'dtype': 'float64',
    'data': new Float64Array( [ NaN ] ),
    'shape': [],
    'strides': [ 0 ],
    'offset': 0,
    'order': 'row-major'
};

var ctx = {
    'count': 0
};

// Perform reduction:
var out = find( [ x, sentinelValue ], isEven, ctx );
// returns 2.0

var count = ctx.count;
// returns 2
```

</section>

<!-- /.usage -->

<section class="notes">

## Notes

-   Each provided ndarray should be an object with the following properties:

    -   **dtype**: data type.
    -   **data**: data buffer.
    -   **shape**: dimensions.
    -   **strides**: stride lengths.
    -   **offset**: index offset.
    -   **order**: specifies whether an ndarray is row-major (C-style) or column major (Fortran-style).

-   The predicate function is provided the following arguments:

    -   **value**: current array element.
    -   **indices**: current array element indices.
    -   **arr**: the input ndarray.

-   For very high-dimensional ndarrays which are non-contiguous, one should consider copying the underlying data to contiguous memory before performing the operation in order to achieve better performance.

</section>

<!-- /.notes -->

<section class="examples">

## Examples

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

```javascript
var discreteUniform = require( '@stdlib/random/array/discrete-uniform' );
var Float64Array = require( '@stdlib/array/float64' );
var ndarray2array = require( '@stdlib/ndarray/base/to-array' );
var find = require( '@stdlib/ndarray/base/find' );

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

var x = {
    'dtype': 'float64',
    'data': discreteUniform( 10, 0.0, 10.0, {
        'dtype': 'float64'
    }),
    'shape': [ 5, 2 ],
    'strides': [ 2, 1 ],
    'offset': 0,
    'order': 'row-major'
};
console.log( ndarray2array( x.data, x.shape, x.strides, x.offset, x.order ) );

var sv = {
    'dtype': 'float64',
    'data': new Float64Array( [ NaN ] ),
    'shape': [],
    'strides': [ 0 ],
    'offset': 0,
    'order': x.order
};
console.log( 'Sentinel Value: %d', sv.data[ 0 ] );

var out = find( [ x, sv ], isEven );
console.log( out );
```

</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">

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

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

</section>

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