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# findLast

> Return a new [ndarray][@stdlib/ndarray/ctor] containing the last elements which pass a test implemented by a predicate function along one or more [ndarray][@stdlib/ndarray/ctor] dimensions.

<section class="intro">

</section>

<!-- /.intro -->

<section class="usage">

## Usage

```javascript
var findLast = require( '@stdlib/ndarray/find-last' );
```

#### findLast( x\[, options], predicate\[, thisArg] )

Returns a new [ndarray][@stdlib/ndarray/ctor] containing the last elements which pass a test implemented by a predicate function along one or more [ndarray][@stdlib/ndarray/ctor] dimensions.

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

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

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

// Create an input ndarray:
var x = array( [ [ [ 1.0, 2.0 ], [ 3.0, 4.0 ] ], [ [ 5.0, 6.0 ], [ 7.0, 8.0 ] ] ] );
// returns <ndarray>

// Perform reduction:
var out = findLast( x, isEven );
// returns <ndarray>[ 8.0 ]
```

The function accepts the following arguments:

-   **x**: input [ndarray][@stdlib/ndarray/ctor].
-   **options**: function options _(optional)_.
-   **predicate**: predicate function.
-   **thisArg**: predicate function execution context _(optional)_.

The function accepts the following options:

-   **dims**: list of dimensions over which to perform a reduction.
-   **keepdims**: boolean indicating whether the reduced dimensions should be included in the returned [ndarray][@stdlib/ndarray/ctor] as singleton dimensions. Default: `false`.
-   **sentinel**: value to return when no element passes the test. May be either a scalar value or a zero-dimensional [ndarray][@stdlib/ndarray/ctor].

By default, the function performs reduction over all elements in a provided [ndarray][@stdlib/ndarray/ctor]. To reduce specific dimensions, set the `dims` option.

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

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

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

// Create an input ndarray:
var x = array( [ [ [ 1.0, 2.0 ], [ 3.0, 4.0 ] ], [ [ 5.0, 6.0 ], [ 7.0, 8.0 ] ] ] );
// returns <ndarray>

var opts = {
    'dims': [ 0 ]
};

// Perform reduction:
var out = findLast( x, opts, isEven );
// returns <ndarray>[ [ NaN, 6.0 ], [ NaN, 8.0 ] ]
```

By default, the function returns an [ndarray][@stdlib/ndarray/ctor] having a shape matching only the non-reduced dimensions of the input [ndarray][@stdlib/ndarray/ctor] (i.e., the reduced dimensions are dropped). To include the reduced dimensions as singleton dimensions in the output [ndarray][@stdlib/ndarray/ctor], set the `keepdims` option to `true`.

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

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

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

// Create an input ndarray:
var x = array( [ [ [ 1.0, 2.0 ], [ 3.0, 4.0 ] ], [ [ 5.0, 6.0 ], [ 7.0, 8.0 ] ] ] );
// returns <ndarray>

var opts = {
    'dims': [ 0 ],
    'keepdims': true
};

// Perform reduction:
var out = findLast( x, opts, isEven );
// returns <ndarray>[ [ [ NaN, 6.0 ], [ NaN, 8.0 ] ] ]
```

To specify a custom sentinel value to return when no element passes the test, set the `sentinel` option.

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

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

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

// Create an input ndarray:
var x = array( [ [ [ 1.0, 3.0 ], [ 5.0, 7.0 ] ], [ [ 9.0, 11.0 ], [ 13.0, 15.0 ] ] ] );
// returns <ndarray>

var opts = {
    'sentinel': -999
};

// Perform reduction:
var out = findLast( x, opts, isEven );
// returns <ndarray>[ -999 ]
```

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

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

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

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

// Create an input ndarray:
var x = array( [ [ [ 1.0, 2.0 ], [ 3.0, 4.0 ] ], [ [ 5.0, 6.0 ], [ 7.0, 8.0 ] ] ] );
// returns <ndarray>

var ctx = {
    'count': 0
};

// Perform reduction:
var out = findLast( x, isEven, ctx );
// returns <ndarray>[ 8.0 ]

var count = ctx.count;
// returns 1
```

#### findLast.assign( x, out\[, options], predicate\[, thisArg] )

Finds the last elements which pass a test implemented by a predicate function along one or more [ndarray][@stdlib/ndarray/ctor] dimensions and assigns results to a provided output [ndarray][@stdlib/ndarray/ctor].

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

```javascript
var array = require( '@stdlib/ndarray/array' );
var empty = require( '@stdlib/ndarray/empty' );
var getDType = require( '@stdlib/ndarray/dtype' );

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

// Create an input ndarray:
var x = array( [ [ [ 1.0, 2.0 ], [ 3.0, 4.0 ] ], [ [ 5.0, 6.0 ], [ 7.0, 8.0 ] ] ] );
// returns <ndarray>

// Create an output ndarray:
var y = empty( [], {
    'dtype': getDType( x )
});

// Perform reduction:
var out = findLast.assign( x, y, isEven );
// returns <ndarray>[ 8.0 ]

var bool = ( out === y );
// returns true
```

The function accepts the following arguments:

-   **x**: input [ndarray][@stdlib/ndarray/ctor].
-   **out**: output [ndarray][@stdlib/ndarray/ctor].
-   **options**: function options _(optional)_.
-   **predicate**: predicate function.
-   **thisArg**: predicate function execution context _(optional)_.

The function accepts the following options:

-   **dims**: list of dimensions over which to perform a reduction.
-   **sentinel**: value to return when no element passes the test. May be either a scalar value or a zero-dimensional [ndarray][@stdlib/ndarray/ctor].

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

```javascript
var array = require( '@stdlib/ndarray/array' );
var empty = require( '@stdlib/ndarray/empty' );
var getDType = require( '@stdlib/ndarray/dtype' );

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

// Create an input ndarray:
var x = array( [ [ [ 1.0, 2.0 ], [ 3.0, 4.0 ] ], [ [ 5.0, 6.0 ], [ 7.0, 8.0 ] ] ] );
// returns <ndarray>

// Create an output ndarray:
var y = empty( [ 2, 2 ], {
    'dtype': getDType( x )
});

var opts = {
    'dims': [ 0 ]
};

// Perform reduction:
var out = findLast.assign( x, y, opts, isEven );
// returns <ndarray>[ [ NaN, 6.0 ], [ NaN, 8.0 ] ]

var bool = ( out === y );
// returns true
```

</section>

<!-- /.usage -->

<section class="notes">

## Notes

-   By default, when no `sentinel` is provided, the function returns a default sentinel value based on the input [ndarray][@stdlib/ndarray/ctor] [data-type][@stdlib/ndarray/dtypes]:

    -   real-valued floating-point data types: `NaN`.
    -   complex-valued floating-point data types: `NaN + NaNj`.
    -   integer data types: maximum value.
    -   boolean data types: `false`.

-   The `predicate` function is provided the following arguments:

    -   **value**: current array element.
    -   **indices**: current array element indices.
    -   **arr**: the input [ndarray][@stdlib/ndarray/ctor].

</section>

<!-- /.notes -->

<section class="examples">

## Examples

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

```javascript
var uniform = require( '@stdlib/random/uniform' );
var isPositive = require( '@stdlib/assert/is-positive-number' ).isPrimitive;
var ndarray2array = require( '@stdlib/ndarray/to-array' );
var findLast = require( '@stdlib/ndarray/find-last' );

var x = uniform( [ 2, 4, 5 ], -10.0, 10.0, {
    'dtype': 'float64'
});
console.log( ndarray2array( x ) );

var y = findLast( x, isPositive );
console.log( y.get() );
```

</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">

[@stdlib/ndarray/ctor]: https://github.com/stdlib-js/ndarray/tree/main/ctor

[@stdlib/ndarray/dtypes]: https://github.com/stdlib-js/ndarray/tree/main/dtypes

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

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

</section>

<!-- /.links -->
