# itermprod
> Create an [iterator][mdn-iterator-protocol] which iteratively computes a moving product.
For a window of size `W`, the moving product is defined as
## Usage
```javascript
var itermprod = require( '@stdlib/stats/iter/mprod' );
```
#### itermprod( iterator, W )
Returns an [iterator][mdn-iterator-protocol] which iteratively computes a moving product. The `W` parameter defines the number of iterated values over which to compute the moving product.
```javascript
var array2iterator = require( '@stdlib/array/to-iterator' );
var arr = array2iterator( [ 2.0, 1.0, 3.0, -7.0, -5.0 ] );
var it = itermprod( arr, 3 );
// Fill the window...
var p = it.next().value; // [2.0]
// returns 2.0
p = it.next().value; // [2.0, 1.0]
// returns 2.0
p = it.next().value; // [2.0, 1.0, 3.0]
// returns 6.0
// Window begins sliding...
p = it.next().value; // [1.0, 3.0, -7.0]
// returns -21.0
p = it.next().value; // [3.0, -7.0, -5.0]
// returns 105.0
```
## Notes
- If an iterated value is non-numeric (including `NaN`), the function returns `NaN` for **at least** `W-1` future invocations. If non-numeric iterated values are possible, you are advised to provide an [`iterator`][mdn-iterator-protocol] which type checks and handles non-numeric values accordingly.
- As `W` values are needed to fill the window buffer, the first `W-1` returned values are calculated from smaller sample sizes. Until the window is full, each returned value is calculated from all previously iterated values.
## Examples
```javascript
var runif = require( '@stdlib/random/iter/uniform' );
var itermprod = require( '@stdlib/stats/iter/mprod' );
// Create an iterator for generating uniformly distributed pseudorandom numbers:
var rand = runif( -10.0, 10.0, {
'seed': 1234,
'iter': 100
});
// Create an iterator for iteratively computing a moving product:
var it = itermprod( rand, 3 );
// Perform manual iteration...
var v;
while ( true ) {
v = it.next();
if ( typeof v.value === 'number' ) {
console.log( 'product: %d', v.value );
}
if ( v.done ) {
break;
}
}
```
[mdn-iterator-protocol]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols#The_iterator_protocol
