npm package: @stdlib/blas-ext-base-dindex-of
Description: Return the first 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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</details>

# dindexOf

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> Return the first 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-dindex-of
```

</section>

<section class="usage">

## Usage

```javascript
var dindexOf = require( '@stdlib/blas-ext-base-dindex-of' );
```

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

Returns the first 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, -1.0, 3.0 ] );

var idx = dindexOf( x.length, 3.0, x, 1 );
// returns 2
```

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 = dindexOf( 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, 4.0, 0.0, -1.0, 3.0 ] );

var idx = dindexOf( 4, -1.0, x, 2 );
// returns 3
```

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( [ 1.0, -2.0, 3.0, -4.0, 5.0, -6.0 ] );

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

// Find index...
var idx = dindexOf( 3, -6.0, x1, 2 );
// returns 2
```

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

Returns the first 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, 0.0, -1.0, 3.0 ] );

var idx = dindexOf.ndarray( x.length, 3.0, x, 1, 0 );
// returns 2
```

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, 3.0, -5.0, 4.0, 0.0, -1.0, 3.0 ] );

var idx = dindexOf.ndarray( 3, 3.0, x, 1, x.length-3 );
// returns 2
```

</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 dindexOf = require( '@stdlib/blas-ext-base-dindex-of' );

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

var idx = dindexOf( x.length, 80.0, x, 1 );
console.log( idx );
```

</section>

<!-- /.examples -->

<!-- C interface documentation. -->

* * *

<section class="c">

## C APIs

<!-- 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 -->

<!-- C usage documentation. -->

<section class="usage">

### Usage

```c
#include "stdlib/blas/ext/base/dindex_of.h"
```

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

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

```c
double x[] = { 1.0, 2.0, 3.0, 4.0 };

int idx = stdlib_strided_dindex_of( 4, 3.0, x, 1 );
// returns 2
```

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

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

Returns the first 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, 4.0 };

int idx = stdlib_strided_dindex_of( 4, 3.0, x, 1, 0 );
// returns 2
```

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_dindex_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/dindex_of.h"
#include <stdio.h>

int main( void ) {
    // Create a strided array:
    double x[] = { 1.0, -2.0, 3.0, -4.0, 5.0, -6.0, 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_dindex_of( N, 5.0, x, strideX );

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

</section>

<!-- /.examples -->

</section>

<!-- /.c -->

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<section class="references">

</section>

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* * *

## 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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