@stdlib/iter/replicate-by/README.md

Standard iterator utilities.

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# iterReplicateBy

> Create an [iterator][mdn-iterator-protocol] which replicates each iterated value according to a provided function.

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## Usage

```javascript
var iterReplicateBy = require( '@stdlib/iter/replicate-by' );
```

#### iterReplicateBy( iterator, fcn\[, thisArg] )

Returns an [iterator][mdn-iterator-protocol] which replicates each iterated value according to a provided function.

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

function fcn( v, i ) {
    return i + 1;
}

var it = iterReplicateBy( array2iterator( [ 1, 2, 3, 4 ] ), fcn );
// returns <Object>

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

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

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

v = it.next().value;
// returns 3

v = it.next().value;
// returns 3

v = it.next().value;
// returns 3

v = it.next().value;
// returns 4

// ...
```

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 three arguments:

-   **value**: iterated value
-   **index**: source iteration index (zero-based)
-   **n**: iteration index (zero-based)

To set the callback execution context, provide a `thisArg`.

<!-- eslint-disable no-invalid-this -->

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

function fcn( v, i ) {
    this.count += 1;
    return i + 1;
}

var ctx = {
    'count': 0
};

var it = iterReplicateBy( array2iterator( [ 1, 2, 3, 4 ] ), fcn, ctx );
// returns <Object>

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

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

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

v = it.next().value;
// returns 3

var count = ctx.count;
// returns 3
```

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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

-   A callback function is invoked **once** per iterated value of the provided [`iterator`][mdn-iterator-protocol].
-   A callback function **must** return an **integer** value. If the return value is less than or equal to `0`, the returned [iterator][mdn-iterator-protocol] skips an iterated value and invokes the callback for the next iterated value of the provided [`iterator`][mdn-iterator-protocol].
-   If an environment supports `Symbol.iterator` **and** a provided [iterator][mdn-iterator-protocol] is iterable, the returned [iterator][mdn-iterator-protocol] is iterable.

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## Examples

<!-- eslint no-undef: "error" -->

```javascript
var randu = require( '@stdlib/random/iter/randu' );
var discreteUniform = require( '@stdlib/random/base/discrete-uniform' );
var iterReplicateBy = require( '@stdlib/iter/replicate-by' );

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

// Create an iterator which replicates each generated number a random number of times:
var it = iterReplicateBy( rand, discreteUniform.factory( 1, 10 ) );

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

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* * *

## See Also

-   <span class="package-name">[`@stdlib/iter/replicate`][@stdlib/iter/replicate]</span><span class="delimiter">: </span><span class="description">create an iterator which replicates each iterated value a specified number of times.</span>

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[mdn-iterator-protocol]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols#The_iterator_protocol

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

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