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README.md

gindexOf

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

Usage

var gindexOf = require( '@stdlib/blas/ext/base/gindex-of' );

gindexOf( N, searchElement, x, strideX )

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

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

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

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 = gindexOf( 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, 4.0, 0.0, -1.0, 3.0 ];

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

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( [ 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 = gindexOf( 3, -6.0, x1, 2 );
// returns 2

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

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

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

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

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

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 gindexOf = require( '@stdlib/blas/ext/base/gindex-of' );

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

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