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dlastIndexOf

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

Installation

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

Alternatively,

• To load the package in a website via a script tag without installation and bundlers, use the ES Module available on the esm branch (see README).
• If you are using Deno, visit the deno branch (see README for usage intructions).
• For use in Observable, or in browser/node environments, use the Universal Module Definition (UMD) build available on the umd branch (see README).

The branches.md file summarizes the available branches and displays a diagram illustrating their relationships.

To view installation and usage instructions specific to each branch build, be sure to explicitly navigate to the respective README files on each branch, as linked to above.

Usage

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.

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.
• strideX: stride length.

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

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:

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 views.

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.

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 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

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

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.

Examples

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 );

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C APIs

Usage

#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.

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.

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.

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.

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 );

Examples

#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 );
}

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Notice

This package is part of 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, see the main project repository.

Community

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License

See LICENSE.

Copyright

Copyright © 2016-2026. The Stdlib Authors.