# incrvariance

Compute an unbiased sample variance incrementally.

## Usage

``````var incrvariance = require( '@stdlib/math/stats/incr/variance' );
``````

#### incrvariance()

Returns an accumulator `function` which incrementally computes an unbiased sample variance.

``````var accumulator = incrvariance();
``````

#### accumulator( [x] )

If provided an input value `x`, the accumulator function returns an updated unbiased sample variance. If not provided an input value `x`, the accumulator function returns the current unbiased sample variance.

``````var s2 = accumulator( 2.0 );
// returns 0.0

s2 = accumulator( 1.0 ); // => ((2-1.5)^2+(1-1.5)^2) / (2-1)
// returns 0.5

s2 = accumulator( 3.0 ); // => ((2-2)^2+(1-2)^2+(3-2)^2) / (3-1)
// returns 1.0

s2 = accumulator();
// returns 1.0
``````

## Notes

• Input values are not type checked. If provided `NaN` or a value which, when used in computations, results in `NaN`, the accumulated value is `NaN` for all future invocations. If non-numeric inputs are possible, you are advised to type check and handle accordingly before passing the value to the accumulator function.

## Examples

``````var randu = require( '@stdlib/random/base/randu' );
var incrvariance = require( '@stdlib/math/stats/incr/variance' );

var accumulator;
var v;
var i;

// Initialize an accumulator:
accumulator = incrvariance();

// For each simulated datum, update the unbiased sample variance...
for ( i = 0; i < 100; i++ ) {
v = randu() * 100.0;
accumulator( v );
}
console.log( accumulator() );
``````