arrayview2iteratorRight

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

Installation

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

Usage

var arrayview2iteratorRight = require( '@stdlib/array-to-view-iterator-right' );

arrayview2iteratorRight( src[, begin[, end]][, mapFcn[, thisArg]] )

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

var it = arrayview2iteratorRight( [ 1, 2, 3, 4 ] );
// returns <Object>

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

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

v = it.next().value;
// returns 2

// ...

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.

The begin and end arguments define the starting (inclusive) and ending (non-inclusive) indices of the array view. By default, the returned iterator starts iterating from the last element in an array-like object (i.e., from the "end"). To specify an alternative view end, provide an end argument (non-inclusive).

var it = arrayview2iteratorRight( [ 1, 2, 3, 4 ], 0, 3 );
// returns <Object>

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

v = it.next().value;
// returns 2

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

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

If end is less than 0, the first iterated value is resolved relative to the last view element. For example, the following generates the same behavior as in the previous example

var it = arrayview2iteratorRight( [ 1, 2, 3, 4 ], 0, -1 );
// returns <Object>

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

v = it.next().value;
// returns 2

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

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

By default, the returned iterator iterates through the first element in an array-like object view. To specify an alternative view beginning, provide a begin argument (inclusive).

var it = arrayview2iteratorRight( [ 1, 2, 3, 4 ], 1 );
// returns <Object>

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

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

v = it.next().value;
// returns 2

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

If begin is less than 0, the last iterated value is resolved relative to the last view element. For example, the following generates the same behavior as in the previous example

var it = arrayview2iteratorRight( [ 1, 2, 3, 4 ], -3 );
// returns <Object>

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

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

v = it.next().value;
// returns 2

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

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

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

var it = arrayview2iteratorRight( [ 1, 2, 3, 4 ], fcn );
// returns <Object>

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

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

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

// ...

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 = arrayview2iteratorRight( [ 1, 2, 3, 4 ], fcn );
// returns <Object>

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

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

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

// ...

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 = arrayview2iteratorRight( [ 1, 2, 3, 4 ], fcn, ctx );
// returns <Object>

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

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

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

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 arrayview2iteratorRight = require( '@stdlib/array-to-view-iterator-right' );

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 from an array view which scales iterated values:
var it = arrayview2iteratorRight( arr, 40, 60, scale );

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

See Also

• @stdlib/array-from-iterator: create (or fill) an array from an iterator.
• @stdlib/array-to-iterator-right: create an iterator from an array-like object, iterating from right to left.
• @stdlib/array-to-strided-iterator: create an iterator from a strided array-like object.
• @stdlib/array-to-view-iterator: create an iterator from an array-like object view.

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 © 2016-2024. The Stdlib Authors.