@stdlib/iter-filter-map NPM

iterFilterMap

Create an iterator which both filters and maps the values of another iterator.

Installation

npm install @stdlib/iter-filter-map

Usage

var iterFilterMap = require( '@stdlib/iter-filter-map' );

iterFilterMap( iterator, fcn[, thisArg] )

Returns an iterator which both filters and maps the values of another iterator according to a callback function.

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

function fcn( v ) {
    if ( v > 2 ) {
        return v * 10;
    }
}

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

var v = it.next().value;
// returns 30

v = it.next().value;
// returns 40

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.

The callback function is provided two arguments:

value: iterated value
index: iteration index (zero-based)

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

function fcn( v, i ) {
    if ( i >= 2 ) {
        return v * 10;
    }
}

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

var v = it.next().value;
// returns 10

v = it.next().value;
// returns 20

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

To set the callback function execution context, provide a thisArg.

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

function fcn( v ) {
    this.count += 1;
    if ( v > 0 ) {
        return v * 10;
    }
}

var ctx = {
    'count': 0
};

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

var v = it.next().value;
// returns 10

v = it.next().value;
// returns 20

v = it.next().value;
// returns 30

var count = ctx.count;
// returns 3

Notes

If the callback function returns undefined, the returned iterator invokes the callback for the next value of the provided iterator. If the callback function returns a value other than undefined, the returned iterator returns the callback's return 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 iterFilterMap = require( '@stdlib/iter-filter-map' );

function fcn( v ) {
    if ( v > 0.5 ) {
        return v * 10.0;
    }
}

// Create a seeded iterator for generating pseudorandom numbers:
var rand = randu({
    'seed': 1234,
    'iter': 20
});

// Create an iterator which both filters and maps the generated numbers:
var it = iterFilterMap( rand, fcn );

// 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.