npm package: @stdlib/blas-ext-base-dlast-index-of
Description: Return the last index of a specified search element in a double-precision floating-point strided array.
Author: The Stdlib Authors
Latest version: 0.1.1

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# dlastIndexOf

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> Return the last index of a specified search element in a double-precision floating-point strided array.

<!-- Section to include introductory text. Make sure to keep an empty line after the intro `section` element and another before the `/section` close. -->

<section class="intro">

</section>

<!-- /.intro -->

<!-- Package usage documentation. -->

<section class="installation">

## Installation

```bash
npm install @stdlib/blas-ext-base-dlast-index-of
```

</section>

<section class="usage">

## Usage

```javascript
var dlastIndexOf = require( '@stdlib/blas-ext-base-dlast-index-of' );
```

#### dlastIndexOf( N, searchElement, x, strideX )

Returns the last index of a specified search element in a double-precision floating-point strided array.

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

var x = new Float64Array( [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, 3.0, -1.0 ] );

var idx = dlastIndexOf( x.length, 3.0, x, 1 );
// returns 6
```

The function has the following parameters:

-   **N**: number of indexed elements.
-   **searchElement**: search element.
-   **x**: input [`Float64Array`][@stdlib/array/float64].
-   **strideX**: stride length.

If the function is unable to find a search element, the function returns `-1`.

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

var x = new Float64Array( [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, 3.0 ] );

var idx = dlastIndexOf( x.length, 8.0, x, 1 );
// returns -1
```

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

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

var x = new Float64Array( [ -2.0, -1.0, 3.0, -5.0, 3.0, 4.0, -1.0, 0.0 ] );

var idx = dlastIndexOf( 4, 3.0, x, 2 );
// returns 2
```

Note that indexing is relative to the first index. To introduce an offset, use [`typed array`][mdn-typed-array] views.

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

// Initial array:
var x0 = new Float64Array( [ -2.0, 3.0, -6.0, -4.0, 5.0, 3.0 ] );

// Create an offset view:
var x1 = new Float64Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element

// Find index:
var idx = dlastIndexOf( 3, 3.0, x1, 2 );
// returns 2
```

#### dlastIndexOf.ndarray( N, searchElement, x, strideX, offsetX )

Returns the last index of a specified search element in a double-precision floating-point strided array using alternative indexing semantics.

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

var x = new Float64Array( [ -2.0, 1.0, 3.0, -5.0, 4.0, 3.0, -1.0, 0.0 ] );

var idx = dlastIndexOf.ndarray( x.length, 3.0, x, 1, 0 );
// returns 5
```

The function has the following additional parameters:

-   **offsetX**: starting index.

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 access only the last three elements of the strided array

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

var x = new Float64Array( [ -2.0, 1.0, 0.0, -5.0, 4.0, 3.0, 3.0, -1.0 ] );

var idx = dlastIndexOf.ndarray( 3, 3.0, x, 1, x.length-3 );
// returns 1
```

</section>

<!-- /.usage -->

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

<section class="notes">

## Notes

-   When searching for a search element, the function checks for equality using the strict equality operator `===`. As a consequence, `NaN` values are considered distinct, and `-0` and `+0` are considered the same.

</section>

<!-- /.notes -->

<!-- Package usage examples. -->

<section class="examples">

## Examples

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

```javascript
var discreteUniform = require( '@stdlib/random-array-discrete-uniform' );
var dlastIndexOf = require( '@stdlib/blas-ext-base-dlast-index-of' );

var x = discreteUniform( 10, -100, 100, {
    'dtype': 'float64'
});
console.log( x );

var idx = dlastIndexOf.ndarray( x.length, 80.0, x, 1, 0 );
console.log( idx );
```

</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/dlast_index_of.h"
```

#### stdlib_strided_dlast_index_of( N, searchElement, \*X, strideX )

Returns the last index of a specified search element in a double-precision floating-point strided array.

```c
double x[] = { 1.0, 2.0, 3.0, 2.0 };

int idx = stdlib_strided_dlast_index_of( 4, 2.0, x, 1 );
// returns 3
```

The function accepts the following arguments:

-   **N**: `[in] CBLAS_INT` number of indexed elements.
-   **searchElement**: `[in] double` search element.
-   **X**: `[in] double*` input array.
-   **strideX**: `[in] CBLAS_INT` stride length.

```c
CBLAS_INT stdlib_strided_dlast_index_of( const CBLAS_INT N, const double searchElement, const double *X, const CBLAS_INT strideX );
```

#### stdlib_strided_dlast_index_of_ndarray( N, searchElement, \*X, strideX, offsetX )

Returns the last index of a specified search element in a double-precision floating-point strided array using alternative indexing semantics.

```c
double x[] = { 1.0, 2.0, 3.0, 2.0 };

int idx = stdlib_strided_dlast_index_of_ndarray( 4, 2.0, x, 1, 0 );
// returns 3
```

The function accepts the following arguments:

-   **N**: `[in] CBLAS_INT` number of indexed elements.
-   **searchElement**: `[in] double` search element.
-   **X**: `[in] double*` input array.
-   **strideX**: `[in] CBLAS_INT` stride length.
-   **offsetX**: `[in] CBLAS_INT` starting index.

```c
CBLAS_INT stdlib_strided_dlast_index_of_ndarray( const CBLAS_INT N, const double searchElement, const double *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">

</section>

<!-- /.notes -->

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

<section class="examples">

### Examples

```c
#include "stdlib/blas/ext/base/dlast_index_of.h"
#include <stdio.h>

int main( void ) {
    // Create a strided array:
    const double x[] = { 1.0, -2.0, 3.0, -4.0, 5.0, 3.0, 7.0, -8.0 };

    // Specify the number of indexed elements:
    const int N = 8;

    // Specify a stride:
    const int strideX = 1;

    // Perform a search:
    int idx = stdlib_strided_dlast_index_of( N, 3.0, x, strideX );

    // Print the result:
    printf( "index value: %d\n", idx );
}
```

</section>

<!-- /.examples -->

</section>

<!-- /.c -->

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</section>

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* * *

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## License

See [LICENSE][stdlib-license].


## Copyright

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

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