sparsearray2iteratorRight

Create an iterator from a sparse array-like object, iterating from right to left.

Installation

npm install @stdlib/array-to-sparse-iterator-right

Alternatively,

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For use in Observable, or in browser/node environments, use the Universal Module Definition (UMD) build available on the umd branch (see README).

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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 sparsearray2iteratorRight = require( '@stdlib/array-to-sparse-iterator-right' );

sparsearray2iteratorRight( src[, mapFcn[, thisArg]] )

Returns an iterator which iterates from right to left over each element in a sparse array-like object.

var it = sparsearray2iteratorRight( [ 1, , , 4 ] );
// returns <Object>

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

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

var bool = it.next().done;
// returns true

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 = sparsearray2iteratorRight( [ 1, 2, , 4 ], fcn );
// returns <Object>

var v = it.next().value;
// returns 40.0

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

// ...

The invoked function is provided three arguments:

value: iterated value.
index: iterated value index.
src: source array-like object.

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

var it = sparsearray2iteratorRight( [ 1, 2, , 4 ], fcn );
// returns <Object>

var v = it.next().value;
// returns 16

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

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

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 = sparsearray2iteratorRight( [ 1, 2, , 4 ], fcn, ctx );
// returns <Object>

var v = it.next().value;
// returns 40.0

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

var count = ctx.count;
// returns 2

Notes

If an environment supports Symbol.iterator, the returned iterator is iterable.
If provided a generic array, the returned iterator ignores holes (i.e., undefined values). To iterate over all generic array elements, use @stdlib/array-to-iterator-right.
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 sparsearray2iteratorRight = require( '@stdlib/array-to-sparse-iterator-right' );

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

// Create an array partially filled with random numbers:
var arr = new Array( 100 );
var i;
for ( i = 0; i < arr.length; i += 2 ) {
    arr[ i ] = randu();
}

// Create an iterator from the array which scales iterated values:
var it = sparsearray2iteratorRight( arr, scale );

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

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.