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Strided Iterator

Create an iterator from a strided array-like object.

Installation

npm install @stdlib/array-to-strided-iterator

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 stridedarray2iterator = require( '@stdlib/array-to-strided-iterator' );

stridedarray2iterator( N, src, stride, offset[, mapFcn[, thisArg]] )

Returns an iterator which iterates over elements in an array-like object according to specified stride parameters.

var values = [ 1, 2, 3, 4, 5, 6, 7, 8 ];

var N = 4;
var stride = -2;
var offset = 6;

var it = stridedarray2iterator( N, values, stride, offset );
// returns <Object>

var v = it.next().value;
// returns 7

v = it.next().value;
// returns 5

v = it.next().value;
// returns 3

// ...

The returned iterator protocol-compliant object has the following properties:

• next: function which returns an iterator protocol-compliant object containing the next iterated value (if one exists) assigned to a value property and a done property having a boolean value indicating whether the iterator is finished.
• return: function which closes an iterator and returns a single (optional) argument in an iterator protocol-compliant object.

To invoke a function for each src value, provide a callback function.

function fcn( v ) {
    return v * 10.0;
}

var it = stridedarray2iterator( 4, [ 1, 2, 3, 4 ], 1, 0, fcn );
// returns <Object>

var v = it.next().value;
// returns 10.0

v = it.next().value;
// returns 20.0

v = it.next().value;
// returns 30.0

// ...

The invoked function is provided four arguments:

• value: iterated value.
• index: iterated value index.
• n: iteration count (zero-based).
• src: source array-like object.

function fcn( v, i ) {
    return v * (i+1);
}

var it = stridedarray2iterator( 4, [ 1, 2, 3, 4 ], 1, 0, fcn );
// returns <Object>

var v = it.next().value;
// returns 1

v = it.next().value;
// returns 4

v = it.next().value;
// returns 9

// ...

To set the callback function execution context, provide a thisArg.

function fcn( v ) {
    this.count += 1;
    return v * 10.0;
}

var ctx = {
    'count': 0
};

var it = stridedarray2iterator( 4, [ 1, 2, 3, 4 ], 1, 0, fcn, ctx );
// returns <Object>

var v = it.next().value;
// returns 10.0

v = it.next().value;
// returns 20.0

v = it.next().value;
// returns 30.0

var count = ctx.count;
// returns 3

Notes

• If an environment supports Symbol.iterator, the returned iterator is iterable.
• If provided a generic array, the returned iterator does not ignore holes. To achieve greater performance for sparse arrays, use a custom iterator.
• A returned iterator does not copy a provided array-like object. To ensure iterable reproducibility, copy a provided array-like object before creating an iterator. Otherwise, any changes to the contents of an array-like object will be reflected in the returned iterator.
• In environments supporting Symbol.iterator, the function explicitly does not invoke an array's @@iterator method, regardless of whether this method is defined. To convert an array to an implementation defined iterator, invoke this method directly.
• The returned iterator supports array-like objects having getter and setter accessors for array element access (e.g., @stdlib/array-complex64).

Examples

var Float64Array = require( '@stdlib/array-float64' );
var inmap = require( '@stdlib/utils-inmap' );
var randu = require( '@stdlib/random-base-randu' );
var stridedarray2iterator = require( '@stdlib/array-to-strided-iterator' );

function scale( v, i ) {
    return v * (i+1);
}

// Create an array filled with random numbers:
var arr = inmap( new Float64Array( 100 ), randu );

// Create an iterator which scales every fourth value in reverse order:
var it = stridedarray2iterator( 25, arr, -4, 99, scale );

// Perform manual iteration...
var v;
while ( true ) {
    v = it.next();
    if ( v.done ) {
        break;
    }
    console.log( v.value );
}

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See Also

• @stdlib/array-from-iterator: create (or fill) an array from an iterator.
• @stdlib/array-to-iterator: create an iterator from an array-like object.

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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 © 2016-2024. The Stdlib Authors.