# iterFilterMap > Create an [iterator][mdn-iterator-protocol] which both filters and maps the values of another [iterator][mdn-iterator-protocol].
## Usage ```javascript var iterFilterMap = require( '@stdlib/iter/filter-map' ); ``` #### iterFilterMap( iterator, fcn\[, thisArg] ) Returns an [iterator][mdn-iterator-protocol] which both filters **and** maps the values of another [`iterator`][mdn-iterator-protocol] according to a callback function. ```javascript 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 var v = it.next().value; // returns 30 v = it.next().value; // returns 40 var bool = it.next().done; // returns true ``` The returned [iterator][mdn-iterator-protocol] protocol-compliant object has the following properties: - **next**: function which returns an [iterator][mdn-iterator-protocol] 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][mdn-iterator-protocol] is finished. - **return**: function which closes an [iterator][mdn-iterator-protocol] and returns a single (optional) argument in an [iterator][mdn-iterator-protocol] protocol-compliant object. The callback function is provided two arguments: - **value**: iterated value. - **index**: iteration index (zero-based). ```javascript 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 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`. ```javascript 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 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][mdn-iterator-protocol] invokes the callback for the next value of the provided [`iterator`][mdn-iterator-protocol]. If the callback function returns a value other than `undefined`, the returned [iterator][mdn-iterator-protocol] returns the callback's return value. - If an environment supports `Symbol.iterator` **and** a provided [iterator][mdn-iterator-protocol] is iterable, the returned [iterator][mdn-iterator-protocol] is iterable.
## Examples ```javascript 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 ); } ```
* * * ## See Also - [`@stdlib/iter/filter`][@stdlib/iter/filter]: create an iterator which filters the values of another iterator according to a predicate function. - [`@stdlib/iter/map`][@stdlib/iter/map]: create an iterator which invokes a function for each iterated value.
[mdn-iterator-protocol]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols#The_iterator_protocol [@stdlib/iter/filter]: https://github.com/stdlib-js/iter/tree/main/filter [@stdlib/iter/map]: https://github.com/stdlib-js/iter/tree/main/map