Package Exports

@stdlib/array-to-view-iterator

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Readme

arrayview2iterator

Create an iterator from an array-like object view.

Installation

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

Usage

var arrayview2iterator = require( '@stdlib/array-to-view-iterator' );

arrayview2iterator( src[, begin[, end]][, mapFcn[, thisArg]] )

Returns an iterator which iterates over each element in an array-like object view.

var it = arrayview2iterator( [ 1, 2, 3, 4 ] );
// returns <Object>

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

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

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.

By default, the returned iterator begins iterating from the first element in an array-like object. To specify an alternative starting index, provide a begin argument (inclusive).

var it = arrayview2iterator( [ 1, 2, 3, 4 ], 1 );
// returns <Object>

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

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

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

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

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

var it = arrayview2iterator( [ 1, 2, 3, 4 ], -3 );
// returns <Object>

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

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

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

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

By default, the returned iterator iterates until the last element in an array-like object. To specify an alternative ending index, provide an end argument (non-inclusive).

var it = arrayview2iterator( [ 1, 2, 3, 4 ], 0, 3 );
// returns <Object>

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

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

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

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

If end is less than 0, the ending index is resolved relative to the last element. For example, the following generates the same behavior as in the previous example

var it = arrayview2iterator( [ 1, 2, 3, 4 ], 0, -1 );
// returns <Object>

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

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

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

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 = arrayview2iterator( [ 1, 2, 3, 4 ], 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 = arrayview2iterator( [ 1, 2, 3, 4 ], 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 = arrayview2iterator( [ 1, 2, 3, 4 ], 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.

Examples

var Float64Array = require( '@stdlib/array-float64' );
var inmap = require( '@stdlib/utils-inmap' );
var randu = require( '@stdlib/random-base-randu' );
var arrayview2iterator = require( '@stdlib/array-to-view-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 from an array view which scales iterated values:
var it = arrayview2iterator( arr, 40, 60, 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.

Community

License

See LICENSE.

@stdlib/array-to-view-iterator