# Strided Iterator > Create an [iterator][mdn-iterator-protocol] from a strided array-like object.
## Usage ```javascript var stridedarray2iterator = require( '@stdlib/array/to-strided-iterator' ); ``` #### stridedarray2iterator( N, src, stride, offset\[, mapFcn\[, thisArg]] ) Returns an [iterator][mdn-iterator-protocol] which iterates over elements in an array-like `object` according to specified stride parameters. ```javascript var values = [ 1, 2, 3, 4, 5, 6, 7, 8 ]; var N = 4; var stride = -2; var offset = 6; var it = stridedarray2iterator( N, values, stride, offset ); // returns var v = it.next().value; // returns 7 v = it.next().value; // returns 5 v = it.next().value; // returns 3 // ... ``` 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 protocol-compliant object. To invoke a function for each `src` value, provide a callback function. ```javascript function fcn( v ) { return v * 10.0; } var it = stridedarray2iterator( 4, [ 1, 2, 3, 4 ], 1, 0, fcn ); // returns var v = it.next().value; // returns 10.0 v = it.next().value; // returns 20.0 v = it.next().value; // returns 30.0 // ... ``` The invoked function is provided four arguments: - `value`: iterated value - `index`: iterated value index - `n`: iteration count (zero-based) - `src`: source array-like object ```javascript function fcn( v, i ) { return v * (i+1); } var it = stridedarray2iterator( 4, [ 1, 2, 3, 4 ], 1, 0, fcn ); // returns var v = it.next().value; // returns 1 v = it.next().value; // returns 4 v = it.next().value; // returns 9 // ... ``` To set the callback function execution context, provide a `thisArg`. ```javascript function fcn( v ) { this.count += 1; return v * 10.0; } var ctx = { 'count': 0 }; var it = stridedarray2iterator( 4, [ 1, 2, 3, 4 ], 1, 0, fcn, ctx ); // returns var v = it.next().value; // returns 10.0 v = it.next().value; // returns 20.0 v = it.next().value; // returns 30.0 var count = ctx.count; // returns 3 ```
## Notes - If an environment supports `Symbol.iterator`, the returned [iterator][mdn-iterator-protocol] is iterable. - If provided a generic `array`, the returned [iterator][mdn-iterator-protocol] does **not** ignore holes. To achieve greater performance for sparse arrays, use a custom [iterator][mdn-iterator-protocol]. - A returned [iterator][mdn-iterator-protocol] does **not** copy a provided array-like `object`. To ensure iterable reproducibility, copy a provided array-like `object` **before** creating an [iterator][mdn-iterator-protocol]. Otherwise, any changes to the contents of an array-like `object` will be reflected in the returned [iterator][mdn-iterator-protocol]. - In environments supporting `Symbol.iterator`, the function **explicitly** does **not** invoke an array's `@@iterator` method, regardless of whether this method is defined. To convert an array to an implementation defined [iterator][mdn-iterator-protocol], invoke this method directly.
## Examples ```javascript var Float64Array = require( '@stdlib/array/float64' ); var inmap = require( '@stdlib/utils/inmap' ); var randu = require( '@stdlib/random/base/randu' ); var stridedarray2iterator = require( '@stdlib/array/to-strided-iterator' ); function scale( v, i ) { return v * (i+1); } // Create an array filled with random numbers: var arr = inmap( new Float64Array( 100 ), randu ); // Create an iterator which scales every fourth value in reverse order: var it = stridedarray2iterator( 25, arr, -4, 99, scale ); // Perform manual iteration... var v; while ( true ) { v = it.next(); if ( v.done ) { break; } console.log( v.value ); } ```
[mdn-iterator-protocol]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols#The_iterator_protocol