# incrwmean
> Compute a [weighted arithmetic mean][weighted-arithmetic-mean] incrementally.
The [weighted arithmetic mean][weighted-arithmetic-mean] is defined as
## Usage
```javascript
var incrwmean = require( '@stdlib/stats/incr/wmean' );
```
#### incrwmean()
Returns an accumulator `function` which incrementally computes a [weighted arithmetic mean][weighted-arithmetic-mean].
```javascript
var accumulator = incrwmean();
```
#### accumulator( \[x, w] )
If provided an input value `x` and a weight `w`, the accumulator function returns an updated weighted mean. If not provided any input values, the accumulator function returns the current mean.
```javascript
var accumulator = incrwmean();
var mu = accumulator( 2.0, 1.0 );
// returns 2.0
mu = accumulator( 2.0, 0.5 );
// returns 2.0
mu = accumulator( 3.0, 1.5 );
// returns 2.5
mu = accumulator();
// returns 2.5
```
## 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
```javascript
var randu = require( '@stdlib/random/base/randu' );
var incrwmean = require( '@stdlib/stats/incr/wmean' );
var accumulator;
var v;
var w;
var i;
// Initialize an accumulator:
accumulator = incrwmean();
// For each simulated datum, update the weighted mean...
for ( i = 0; i < 100; i++ ) {
v = randu() * 100.0;
w = randu() * 100.0;
accumulator( v, w );
}
console.log( accumulator() );
```
[weighted-arithmetic-mean]: https://en.wikipedia.org/wiki/Weighted_arithmetic_mean
