@stdlib/iter-slice NPM

iterSlice

Create an iterator which returns a subsequence of iterated values from a provided iterator.

Installation

npm install @stdlib/iter-slice

Usage

var iterSlice = require( '@stdlib/iter-slice' );

iterSlice( iterator[, begin[, end]] )

Returns an iterator which returns a subsequence of iterated values from a provided iterator.

var array2iterator = require( '@stdlib/array-to-iterator' );

var it = iterSlice( array2iterator( [ 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 returns a provided iterator's first iterated value through an iterator's last iterated value. To specify an alternative start iteration index (zero-based and inclusive), provide a begin argument.

var array2iterator = require( '@stdlib/array-to-iterator' );

var it = iterSlice( array2iterator( [ 1, 2, 3, 4 ] ), 2 );
// returns <Object>

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

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

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

By default, the returned iterator continues iterating until it consumes all of a provided iterator's iterated values. To specify an end iteration index (zero-based and non-inclusive), provide an end argument.

var array2iterator = require( '@stdlib/array-to-iterator' );

var it = iterSlice( array2iterator( [ 1, 2, 3, 4 ] ), 1, 3 );
// returns <Object>

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

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

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

If begin is greater than or equal to end, the returned iterator does not return any iterated values.

var array2iterator = require( '@stdlib/array-to-iterator' );

var it = iterSlice( array2iterator( [ 1, 2, 3, 4 ] ), 3, 1 );
// returns <Object>

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

Notes

If an environment supports Symbol.iterator and a provided iterator is iterable, the returned iterator is iterable.

Examples

var randu = require( '@stdlib/random-iter-randu' );
var iterSlice = require( '@stdlib/iter-slice' );

// Create a seeded iterator for generating pseudorandom numbers:
var rand = randu({
    'seed': 1234
});

// Create an iterator which returns a subsequence of 10 generated numbers:
var it = iterSlice( rand, 10, 20 );

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