# itervariance
> Compute the [unbiased sample variance][sample-variance] over all [iterated][mdn-iterator-protocol] values.
The [unbiased sample variance][sample-variance] is defined as
## Usage
```javascript
var itervariance = require( '@stdlib/stats/iter/variance' );
```
#### itervariance( iterator\[, mean] )
Computes the [unbiased sample variance][sample-variance] over all [iterated][mdn-iterator-protocol] values.
```javascript
var array2iterator = require( '@stdlib/array/to-iterator' );
var arr = array2iterator( [ 2.0, 1.0, 3.0 ] );
var s2 = itervariance( arr );
// returns 1.0
```
If the mean is already known, provide a `mean` argument.
```javascript
var array2iterator = require( '@stdlib/array/to-iterator' );
var arr = array2iterator( [ 2.0, 1.0, 3.0 ] );
var s2 = itervariance( arr, 2.0 );
// returns ~0.67
```
## Notes
- If an iterated value is non-numeric (including `NaN`), the returned [`iterator`][mdn-iterator-protocol] returns `NaN`. 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.
## Examples
```javascript
var runif = require( '@stdlib/random/iter/uniform' );
var itervariance = require( '@stdlib/stats/iter/variance' );
// Create an iterator for generating uniformly distributed pseudorandom numbers:
var rand = runif( -10.0, 10.0, {
'seed': 1234,
'iter': 100
});
// Compute the unbiased sample variance:
var s2 = itervariance( rand );
// returns
console.log( 'Variance: %d.', s2 );
```
[sample-variance]: https://en.wikipedia.org/wiki/Variance
[mdn-iterator-protocol]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols#The_iterator_protocol
