@stdlib/iter-strided-by NPM

iterStridedBy

Create an iterator which steps according to a provided callback function.

Installation

npm install @stdlib/iter-strided-by

Usage

var iterStridedBy = require( '@stdlib/iter-strided-by' );

iterStridedBy( iterator, fcn[, offset[, eager]][, thisArg] )

Returns an iterator which steps according to a provided callback function.

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

function stride( v, i ) {
    return (i % 10) + 1;
}

var arr = array2iterator( [ 1, 2, 3, 4, 5, 6, 7, 8 ] );
var it = iterStridedBy( arr, stride );
// returns <Object>

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

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

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

// ...

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 callback function is provided four arguments:

value: iterated value
i: source iteration index (zero-based)
n: iteration index (zero-based)
curr: current stride

To set the callback execution context, provide a thisArg.

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

function stride( v, i ) {
    this.count += 1;
    return (i % 10) + 1;
}

var ctx = {
    'count': 0
};

var arr = array2iterator( [ 1, 2, 3, 4, 5, 6, 7, 8 ] );
var it = iterStridedBy( arr, stride, ctx );
// returns <Object>

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

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

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

v = it.next().value;
// returns 8

var count = ctx.count;
// returns 4

To skip the first N values of a provided iterator, provide an offset argument.

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

function stride( v, i ) {
    return (i % 10) + 1;
}

var arr = array2iterator( [ 1, 2, 3, 4, 5, 6, 7, 8 ] );
var it = iterStridedBy( arr, stride, 1 );
// returns <Object>

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

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

r = it.next().value;
// returns 8

// ...

By default, the returned iterator defers consuming the first N input iterator values until the first value of the returned iterator is consumed. To eagerly advance the input iterator, set the eager argument to true.

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

function stride() {
    return 1;
}

var arr = array2iterator( [ 1, 2, 3, 4, 5, 6, 7, 8 ] );
var it = iterStridedBy( arr, stride, 4, true );
// returns <Object>

var r = it.next().value;
// returns 5

r = it.next().value;
// returns 6

r = it.next().value;
// returns 7

// ...

Notes

A callback function must return a positive integer value.
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 discreteUniform = require( '@stdlib/random-base-discrete-uniform' ).factory;
var iterStridedBy = require( '@stdlib/iter-strided-by' );

// Create a seeded iterator for generating pseudorandom numbers:
var rand = randu({
    'seed': 1234,
    'iter': 10
});

// Create a PRNG for generating pseudorandom integers on the interval [1,10]:
var randi = discreteUniform( 1, 10, {
    'seed': 4321
});

// Create an iterator which randomly selects input iterator values:
var it = iterStridedBy( rand, randi );

// 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.