# Iterators

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> Standard library iterator utilities.

## Installation

```bash
npm install @stdlib/iter
```


## Usage

```javascript
var ns = require( '@stdlib/iter' );
```

#### ns

Standard library iterator utilities.

```javascript
var objectKeys = require( '@stdlib/utils/keys' );

var keys = objectKeys( ns );
// e.g., returns [ 'iterAny', 'iterAnyBy', ... ]
```


-   [`iterAdvance( iterator[, n] )`][@stdlib/iter/advance]: advance an iterator.
-   [`iterAnyBy( iterator, predicate[, thisArg] )`][@stdlib/iter/any-by]: test whether at least one iterated value passes a test implemented by a predicate function.
-   [`iterAny( iterator )`][@stdlib/iter/any]: test whether at least one iterated value is truthy.
-   [`iterConcat( iter0, ...iterator )`][@stdlib/iter/concat]: create an iterator which iterates over the values of two or more iterators.
-   [`iterConstant( value[, options] )`][@stdlib/iter/constant]: create an iterator which always returns the same value.
-   [`iterCounter( iterator )`][@stdlib/iter/counter]: create an iterator which iteratively computes the number of iterated values.
-   [`iterDatespace( start, stop[, N][, options] )`][@stdlib/iter/datespace]: create an iterator which returns evenly spaced dates over a specified interval.
-   [`iterDedupeBy( iterator, [limit,] fcn )`][@stdlib/iter/dedupe-by]: create an iterator which removes consecutive values that resolve to the same value according to a provided function.
-   [`iterDedupe( iterator[, limit] )`][@stdlib/iter/dedupe]: create an iterator which removes consecutive duplicated values.
-   [`iterEmpty()`][@stdlib/iter/empty]: create an empty iterator.
-   [`iterEveryBy( iterator, predicate[, thisArg] )`][@stdlib/iter/every-by]: test whether every iterated value passes a test implemented by a predicate function.
-   [`iterEvery( iterator )`][@stdlib/iter/every]: test whether all iterated values are truthy.
-   [`iterFill( iterator, value[, begin[, end]] )`][@stdlib/iter/fill]: create an iterator which replaces all values from a provided iterator from a start index to an end index with a static value.
-   [`iterFilterMap( iterator, fcn[, thisArg] )`][@stdlib/iter/filter-map]: create an iterator which both filters and maps the values of another iterator.
-   [`iterFilter( iterator, predicate[, thisArg] )`][@stdlib/iter/filter]: create an iterator which filters the values of another iterator according to a predicate function.
-   [`iterFirst( iterator )`][@stdlib/iter/first]: return the first iterated value.
-   [`iterFlow( methods )`][@stdlib/iter/flow]: create a fluent interface for chaining together iterator methods.
-   [`iterForEach( iterator, fcn[, thisArg] )`][@stdlib/iter/for-each]: create an iterator which invokes a function for each iterated value before returning the iterated value.
-   [`iterHead( iterator, n )`][@stdlib/iter/head]: create an iterator which returns the first `n` values of a provided iterator.
-   [`iterIncrspace( start, stop[, increment] )`][@stdlib/iter/incrspace]: create an iterator which returns evenly spaced numbers according to a specified increment.
-   [`iterIntersectionByHash( iter0, ...iterator, hashFcn[, thisArg] )`][@stdlib/iter/intersection-by-hash]: create an iterator which returns the intersection of two or more iterators according to a hash function.
-   [`iterIntersection( iter0, ...iterator )`][@stdlib/iter/intersection]: create an iterator which returns the intersection of two or more iterators.
-   [`iterLast( iterator )`][@stdlib/iter/last]: consume an entire iterator and return the last iterated value.
-   [`iterLength( iterator )`][@stdlib/iter/length]: return an iterator's length.
-   [`iterLinspace( start, stop[, N] )`][@stdlib/iter/linspace]: create an iterator which returns evenly spaced numbers over a specified interval.
-   [`iterLogspace( start, stop[, N][, options] )`][@stdlib/iter/logspace]: create an iterator which returns evenly spaced numbers over a specified interval.
-   [`iterMap( iterator, fcn[, thisArg] )`][@stdlib/iter/map]: create an iterator which invokes a function for each iterated value.
-   [`iterMapN( iter0, ...iterator, fcn[, thisArg] )`][@stdlib/iter/mapn]: create an iterator which transforms iterated values from two or more iterators by applying the iterated values as arguments to a provided function.
-   [`iterNoneBy( iterator, predicate[, thisArg] )`][@stdlib/iter/none-by]: test whether every iterated value fails a test implemented by a predicate function.
-   [`iterNone( iterator )`][@stdlib/iter/none]: test whether all iterated values are falsy.
-   [`iterNth( iterator, n )`][@stdlib/iter/nth]: return the nth iterated value.
-   [`iterThunk( iterFcn[, ...args] )`][@stdlib/iter/pipeline-thunk]: create an iterator "thunk".
-   [`iterPipeline( iterFcn0[, ...iterFcn] )`][@stdlib/iter/pipeline]: create an iterator pipeline.
-   [`iterPop( iterator[, clbk[, thisArg]] )`][@stdlib/iter/pop]: create an iterator which skips the last value of a provided iterator.
-   [`iterPush( iterator, ...items )`][@stdlib/iter/push]: create an iterator which appends additional values to the end of a provided iterator.
-   [`iterReject( iterator, predicate[, thisArg] )`][@stdlib/iter/reject]: create an iterator which rejects the values of another iterator according to a predicate function.
-   [`iterReplicateBy( iterator, fcn[, thisArg] )`][@stdlib/iter/replicate-by]: create an iterator which replicates each iterated value according to a provided function.
-   [`iterReplicate( iterator, n )`][@stdlib/iter/replicate]: create an iterator which replicates each iterated value a specified number of times.
-   [`iterShift( iterator[, clbk[, thisArg]] )`][@stdlib/iter/shift]: create an iterator which skips the first value of a provided iterator.
-   [`iterSlice( iterator[, begin[, end]] )`][@stdlib/iter/slice]: create an iterator which returns a subsequence of iterated values from a provided iterator.
-   [`iterSomeBy( iterator, n, predicate[, thisArg] )`][@stdlib/iter/some-by]: test whether at least `n` iterated values pass a test implemented by a predicate function.
-   [`iterSome( iterator, n )`][@stdlib/iter/some]: test whether at least `n` iterated values are truthy.
-   [`iterStep( start, increment[, N] )`][@stdlib/iter/step]: create an iterator which returns a sequence of numbers according to a specified increment.
-   [`iterStridedBy( iterator, fcn[, offset[, eager]][, thisArg] )`][@stdlib/iter/strided-by]: create an iterator which steps according to a provided callback function.
-   [`iterStrided( iterator, stride[, offset[, eager]] )`][@stdlib/iter/strided]: create an iterator which steps by a specified amount.
-   [`iterator2arrayviewRight( iterator, dest[, begin[, end]][, mapFcn[, thisArg]] )`][@stdlib/iter/to-array-view-right]: fill an array-like object view from right to left with values returned from an iterator.
-   [`iterator2arrayview( iterator, dest[, begin[, end]][, mapFcn[, thisArg]] )`][@stdlib/iter/to-array-view]: fill an array-like object view with values returned from an iterator.
-   [`iterUnion( iter0, ...iterator )`][@stdlib/iter/union]: create an iterator which returns the union of two or more iterators.
-   [`iterUniqueByHash( iterator, hashFcn[, thisArg] )`][@stdlib/iter/unique-by-hash]: create an iterator which returns unique values according to a hash function.
-   [`iterUniqueBy( iterator, predicate[, thisArg] )`][@stdlib/iter/unique-by]: create an iterator which returns unique values according to a predicate function.
-   [`iterUnique( iterator )`][@stdlib/iter/unique]: create an iterator which returns unique values.
-   [`iterUnitspace( start[, stop] )`][@stdlib/iter/unitspace]: create an iterator which returns numbers incremented by `1`.
-   [`iterUnshift( iterator, ...items )`][@stdlib/iter/unshift]: create an iterator which prepends values to the beginning of a provided iterator.

## Examples

```javascript
var objectKeys = require( '@stdlib/utils/keys' );
var uncapitalize = require( '@stdlib/string/uncapitalize' );
var replace = require( '@stdlib/string/replace' );
var contains = require( '@stdlib/assert/contains' );
var randu = require( '@stdlib/random/iter/randu' );
var ns = require( '@stdlib/iter' );

// Create a fluent interface for chaining together iterator operations...

// Retrieve all the iterator utility names:
var keys = objectKeys( ns );

// Define a list of utilities to exclude from the fluent API:
var exclude = [ 'iterFlow', 'iterPipeline', 'iterThunk' ];

// Map each utility name to a fluent interface method...
var methods = {};
var key;
var k;
var i;
for ( i = 0; i < keys.length; i++ ) {
    key = keys[ i ];
    if ( contains( exclude, key ) ) {
        continue;
    }
    k = uncapitalize( replace( key, /^iter/, '' ) );
    methods[ k ] = ns[ key ];
}

// Create a fluent interface:
var FluentIterator = ns.iterFlow( methods );

// Create a new fluent interface iterator:
var it1 = new FluentIterator( randu() );

// Define a predicate function for filtering values:
function predicate( v ) {
    return ( v > 0.25 && v < 0.75 );
}

// Define a function which transforms iterated values:
function transform( v ) {
    return v * 10.0;
}

// Define a function to be invoked for each iterated value:
function log( v ) {
    console.log( v );
}

// Chain together a sequence of operations:
var it2 = it1.filter( predicate )
    .map( transform )
    .head( 10 )
    .forEach( log );

// Perform manual iteration...
var v;
while ( true ) {
    v = it2.next();
    if ( v.done ) {
        break;
    }
}
```


* * *

## Notice

This package is part of [stdlib][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][stdlib], see the main project [repository][stdlib].

#### Community

[![Chat][chat-image]][chat-url]

---

## License

See [LICENSE][stdlib-license].

## Copyright

Copyright © 2016-2021. The Stdlib [Authors][stdlib-authors].

[npm-image]: http://img.shields.io/npm/v/@stdlib/iter.svg
[npm-url]: https://npmjs.org/package/@stdlib/iter

[test-image]: https://github.com/stdlib-js/iter/actions/workflows/test.yml/badge.svg
[test-url]: https://github.com/stdlib-js/iter/actions/workflows/test.yml

[coverage-image]: https://img.shields.io/codecov/c/github/stdlib-js/iter/main.svg
[coverage-url]: https://codecov.io/github/stdlib-js/iter?branch=main

[dependencies-image]: https://img.shields.io/david/stdlib-js/iter.svg
[dependencies-url]: https://david-dm.org/stdlib-js/iter/main

[chat-image]: https://img.shields.io/gitter/room/stdlib-js/stdlib.svg
[chat-url]: https://gitter.im/stdlib-js/stdlib/

[stdlib]: https://github.com/stdlib-js/stdlib

[stdlib-authors]: https://github.com/stdlib-js/stdlib/graphs/contributors

[stdlib-license]: https://raw.githubusercontent.com/stdlib-js/iter/main/LICENSE

[@stdlib/iter/advance]: https://github.com/stdlib-js/iter/tree/main/advance

[@stdlib/iter/any-by]: https://github.com/stdlib-js/iter/tree/main/any-by

[@stdlib/iter/any]: https://github.com/stdlib-js/iter/tree/main/any

[@stdlib/iter/concat]: https://github.com/stdlib-js/iter/tree/main/concat

[@stdlib/iter/constant]: https://github.com/stdlib-js/iter/tree/main/constant

[@stdlib/iter/counter]: https://github.com/stdlib-js/iter/tree/main/counter

[@stdlib/iter/datespace]: https://github.com/stdlib-js/iter/tree/main/datespace

[@stdlib/iter/dedupe-by]: https://github.com/stdlib-js/iter/tree/main/dedupe-by

[@stdlib/iter/dedupe]: https://github.com/stdlib-js/iter/tree/main/dedupe

[@stdlib/iter/empty]: https://github.com/stdlib-js/iter/tree/main/empty

[@stdlib/iter/every-by]: https://github.com/stdlib-js/iter/tree/main/every-by

[@stdlib/iter/every]: https://github.com/stdlib-js/iter/tree/main/every

[@stdlib/iter/fill]: https://github.com/stdlib-js/iter/tree/main/fill

[@stdlib/iter/filter-map]: https://github.com/stdlib-js/iter/tree/main/filter-map

[@stdlib/iter/filter]: https://github.com/stdlib-js/iter/tree/main/filter

[@stdlib/iter/first]: https://github.com/stdlib-js/iter/tree/main/first

[@stdlib/iter/flow]: https://github.com/stdlib-js/iter/tree/main/flow

[@stdlib/iter/for-each]: https://github.com/stdlib-js/iter/tree/main/for-each

[@stdlib/iter/head]: https://github.com/stdlib-js/iter/tree/main/head

[@stdlib/iter/incrspace]: https://github.com/stdlib-js/iter/tree/main/incrspace

[@stdlib/iter/intersection-by-hash]: https://github.com/stdlib-js/iter/tree/main/intersection-by-hash

[@stdlib/iter/intersection]: https://github.com/stdlib-js/iter/tree/main/intersection

[@stdlib/iter/last]: https://github.com/stdlib-js/iter/tree/main/last

[@stdlib/iter/length]: https://github.com/stdlib-js/iter/tree/main/length

[@stdlib/iter/linspace]: https://github.com/stdlib-js/iter/tree/main/linspace

[@stdlib/iter/logspace]: https://github.com/stdlib-js/iter/tree/main/logspace

[@stdlib/iter/map]: https://github.com/stdlib-js/iter/tree/main/map

[@stdlib/iter/mapn]: https://github.com/stdlib-js/iter/tree/main/mapn

[@stdlib/iter/none-by]: https://github.com/stdlib-js/iter/tree/main/none-by

[@stdlib/iter/none]: https://github.com/stdlib-js/iter/tree/main/none

[@stdlib/iter/nth]: https://github.com/stdlib-js/iter/tree/main/nth

[@stdlib/iter/pipeline-thunk]: https://github.com/stdlib-js/iter/tree/main/pipeline-thunk

[@stdlib/iter/pipeline]: https://github.com/stdlib-js/iter/tree/main/pipeline

[@stdlib/iter/pop]: https://github.com/stdlib-js/iter/tree/main/pop

[@stdlib/iter/push]: https://github.com/stdlib-js/iter/tree/main/push

[@stdlib/iter/reject]: https://github.com/stdlib-js/iter/tree/main/reject

[@stdlib/iter/replicate-by]: https://github.com/stdlib-js/iter/tree/main/replicate-by

[@stdlib/iter/replicate]: https://github.com/stdlib-js/iter/tree/main/replicate

[@stdlib/iter/shift]: https://github.com/stdlib-js/iter/tree/main/shift

[@stdlib/iter/slice]: https://github.com/stdlib-js/iter/tree/main/slice

[@stdlib/iter/some-by]: https://github.com/stdlib-js/iter/tree/main/some-by

[@stdlib/iter/some]: https://github.com/stdlib-js/iter/tree/main/some

[@stdlib/iter/step]: https://github.com/stdlib-js/iter/tree/main/step

[@stdlib/iter/strided-by]: https://github.com/stdlib-js/iter/tree/main/strided-by

[@stdlib/iter/strided]: https://github.com/stdlib-js/iter/tree/main/strided

[@stdlib/iter/to-array-view-right]: https://github.com/stdlib-js/iter/tree/main/to-array-view-right

[@stdlib/iter/to-array-view]: https://github.com/stdlib-js/iter/tree/main/to-array-view

[@stdlib/iter/union]: https://github.com/stdlib-js/iter/tree/main/union

[@stdlib/iter/unique-by-hash]: https://github.com/stdlib-js/iter/tree/main/unique-by-hash

[@stdlib/iter/unique-by]: https://github.com/stdlib-js/iter/tree/main/unique-by

[@stdlib/iter/unique]: https://github.com/stdlib-js/iter/tree/main/unique

[@stdlib/iter/unitspace]: https://github.com/stdlib-js/iter/tree/main/unitspace

[@stdlib/iter/unshift]: https://github.com/stdlib-js/iter/tree/main/unshift

