time-to-botec/js/node_modules/@stdlib/stats/iter/variance/README.md

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# itervariance

> Compute the [unbiased sample variance][sample-variance] over all [iterated][mdn-iterator-protocol] values.

<section class="intro">

The [unbiased sample variance][sample-variance] is defined as

<!-- <equation class="equation" label="eq:unbiased_sample_variance" align="center" raw="s^2 = \frac{1}{n-1} \sum_{i=0}^{n-1} ( x_i - \bar{x} )^2" alt="Equation for the unbiased sample variance."> -->

<div class="equation" align="center" data-raw-text="s^2 = \frac{1}{n-1} \sum_{i=0}^{n-1} ( x_i - \bar{x} )^2" data-equation="eq:unbiased_sample_variance">
    <img src="https://cdn.jsdelivr.net/gh/stdlib-js/stdlib@e7ac225deb396ee6d2b4d5fc1a2faa645582349f/lib/node_modules/@stdlib/stats/iter/variance/docs/img/equation_unbiased_sample_variance.svg" alt="Equation for the unbiased sample variance.">
    <br>
</div>

<!-- </equation> -->

</section>

<!-- /.intro -->

<!-- Package usage documentation. -->

<section class="usage">

## 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
```

</section>

<!-- /.usage -->

<!-- Package usage notes. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->

<section class="notes">

## 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.

</section>

<!-- /.notes -->

<!-- Package usage examples. -->

<section class="examples">

## Examples

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

```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 <number>

console.log( 'Variance: %d.', s2 );
```

</section>

<!-- /.examples -->

<!-- Section to include cited references. If references are included, add a horizontal rule *before* the section. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->

<section class="references">

</section>

<!-- /.references -->

<!-- Section for all links. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->

<section class="links">

[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

</section>

<!-- /.links -->