glastIndexOf

Return the last index of a specified search element in a strided array.

Installation

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

Usage

var glastIndexOf = require( '@stdlib/blas-ext-base-glast-index-of' );

glastIndexOf( N, searchElement, x, strideX )

Returns the last index of a specified search element in a strided array.

var x = [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, 3.0, -1.0 ];

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

The function has the following parameters:

• N: number of indexed elements.
• searchElement: search element.
• x: input array.
• strideX: stride length.

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

var x = [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, 3.0 ];

var idx = glastIndexOf( 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 x = [ -2.0, -1.0, 3.0, -5.0, 3.0, 4.0, -1.0, 0.0 ];

var idx = glastIndexOf( 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 = glastIndexOf( 3, 3.0, x1, 2 );
// returns 2

glastIndexOf.ndarray( N, searchElement, x, strideX, offsetX )

Returns the last index of a specified search element in a strided array using alternative indexing semantics.

var x = [ -2.0, 1.0, 3.0, -5.0, 4.0, 3.0, -1.0, 0.0 ];

var idx = glastIndexOf.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 x = [ -2.0, 1.0, 0.0, -5.0, 4.0, 3.0, 3.0, -1.0 ];

var idx = glastIndexOf.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.
• Both functions support array-like objects having getter and setter accessors for array element access (e.g., @stdlib/array-base/accessor).

Examples

var discreteUniform = require( '@stdlib/random-array-discrete-uniform' );
var glastIndexOf = require( '@stdlib/blas-ext-base-glast-index-of' );

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

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

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

License

See LICENSE.

Copyright

Copyright © 2016-2026. The Stdlib Authors.