time-to-botec/js/node_modules/@stdlib/array/to-strided-iterator/README.md

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@license Apache-2.0
Copyright (c) 2018 The Stdlib Authors.
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# Strided Iterator
> Create an [iterator][mdn-iterator-protocol] from a strided array-like object.
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</section>
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<section class="usage">
## 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 <Object>
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 <Object>
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 <Object>
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 <Object>
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
```
</section>
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<!-- Package usage notes. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->
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## 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.
</section>
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## Examples
<!-- eslint no-undef: "error" -->
```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 );
}
```
</section>
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</section>
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<section class="links">
[mdn-iterator-protocol]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols#The_iterator_protocol
</section>
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