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gfirstIndexEqual

Return the index of the first element in a strided array equal to a corresponding element in another strided array.

Installation

npm install @stdlib/blas-ext-base-gfirst-index-equal

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 gfirstIndexEqual = require( '@stdlib/blas-ext-base-gfirst-index-equal' );

gfirstIndexEqual( N, x, strideX, y, strideY )

Returns the index of the first element in a strided array equal to a corresponding element in another strided array.

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

var idx = gfirstIndexEqual( x.length, x, 1, y, 1 );
// returns 2

The function has the following parameters:

• N: number of indexed elements.
• x: first input array.
• strideX: stride length for x.
• y: second input array.
• strideY: stride length for y.

If the function is unable to find matching elements, the function returns -1.

var x = [ 1.0, 2.0, 3.0, 4.0 ];
var y = [ 5.0, 6.0, 7.0, 8.0 ];

var idx = gfirstIndexEqual( x.length, x, 1, y, 1 );
// returns -1

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

var x = [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ];
var y = [ 0.0, 0.0, 3.0, 0.0, 0.0, 0.0 ];

var idx = gfirstIndexEqual( 3, x, 2, y, 2 );
// returns 1

Note that indexing is relative to the first index. To introduce an offset, use typed array views.

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

// Initial arrays...
var x0 = new Float64Array( [ 1.0, 2.0, 3.0, 4.0 ] );
var y0 = new Float64Array( [ 0.0, 0.0, 3.0, 0.0 ] );

// Create offset views...
var x1 = new Float64Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element
var y1 = new Float64Array( y0.buffer, y0.BYTES_PER_ELEMENT*1 ); // start at 2nd element

// Find index...
var idx = gfirstIndexEqual( 2, x1, 1, y1, 1 );
// returns 1

gfirstIndexEqual.ndarray( N, x, strideX, offsetX, y, strideY, offsetY )

Returns the index of the first element in a strided array equal to a corresponding element in another strided array using alternative indexing semantics.

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

var idx = gfirstIndexEqual.ndarray( x.length, x, 1, 0, y, 1, 0 );
// returns 2

The function has the following additional parameters:

• offsetX: starting index for x.
• offsetY: starting index for y.

While typed array views mandate a view offset based on the underlying buffer, the offset parameters support indexing semantics based on starting indices. For example, to access only the last three elements of each strided array:

var x = [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ];
var y = [ 0.0, 0.0, 0.0, 4.0, 5.0, 6.0 ];

var idx = gfirstIndexEqual.ndarray( 3, x, 1, x.length-3, y, 1, y.length-3 );
// returns 0

Notes

• When comparing elements, 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 gfirstIndexEqual = require( '@stdlib/blas-ext-base-gfirst-index-equal' );

var x = discreteUniform( 10, 0, 10, {
    'dtype': 'generic'
});
console.log( x );

var y = discreteUniform( 10, 0, 10, {
    'dtype': 'generic'
});
console.log( y );

var idx = gfirstIndexEqual( x.length, x, 1, y, 1 );
console.log( 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.