iterWhileEach

Create an iterator which, while a test condition is true, invokes a function for each iterated value before returning the iterated value.

Installation

npm install @stdlib/iter-while-each

Usage

var iterWhileEach = require( '@stdlib/iter-while-each' );

iterWhileEach( iterator, predicate, fcn[, thisArg] )

Returns an iterator which invokes a function for each iterated value before returning the iterated value until either a predicate function returns false or the iterator has iterated over all values.

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

function predicate( v ) {
    return v < 3;
}

function assert( v ) {
    if ( v !== v ) {
        throw new Error( 'should not be NaN' );
    }
}

var it = iterWhileEach( array2iterator( [ 1, 2, 3, 4 ] ), predicate, assert );
// returns {}

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

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

r = it.next().value;
// undefined

// ...

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.

Both the predicate function and the function to invoke for each iterated value are provided two arguments:

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

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

function predicate( v ) {
    return v < 3;
}

function assert( v, i ) {
    if ( i > 1 ) {
        throw new Error( 'unexpected error' );
    }
}

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

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

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

r = it.next().value;
// undefined

// ...

To set the execution context for fcn, provide a thisArg.

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

function assert( v ) {
    this.count += 1;
    if ( v !== v ) {
        throw new Error( 'should not be NaN' );
    }
}

function predicate( v ) {
    return v < 3;
}

var ctx = {
    'count': 0
};

var it = iterWhileEach( array2iterator( [ 1, 2, 3 ] ), predicate, assert, ctx );
// returns <Object>

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

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

var count = ctx.count;
// returns 2

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 isnan = require( '@stdlib/math-base-assert-is-nan' );
var iterWhileEach = require( '@stdlib/iter-while-each' );

function assert( v ) {
    if ( isnan( v ) ) {
        throw new Error( 'should not be NaN' );
    }
}

function predicate( v ) {
    return v <= 0.75;
}

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

// Create an iterator which validates generated numbers:
var it = iterWhileEach( rand, predicate, assert );

// 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.

Community

License

See LICENSE.

Copyright

Copyright © 2016-2024. The Stdlib Authors.