# @stdlib/stats-incr-stdev

0.2.2 • Public • Published

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# incrstdev

Compute a corrected sample standard deviation incrementally.

The corrected sample standard deviation is defined as

## Installation

`npm install @stdlib/stats-incr-stdev`

## Usage

`var incrstdev = require( '@stdlib/stats-incr-stdev' );`

#### incrstdev( [mean] )

Returns an accumulator `function` which incrementally computes a corrected sample standard deviation.

`var accumulator = incrstdev();`

If the mean is already known, provide a `mean` argument.

`var accumulator = incrstdev( 3.0 );`

#### accumulator( [x] )

If provided an input value `x`, the accumulator function returns an updated corrected sample standard deviation. If not provided an input value `x`, the accumulator function returns the current corrected sample standard deviation.

```var accumulator = incrstdev();

var s = accumulator( 2.0 );
// returns 0.0

s = accumulator( 1.0 ); // => sqrt(((2-1.5)^2+(1-1.5)^2) / (2-1))
// returns ~0.7071

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

s = 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 incrstdev = require( '@stdlib/stats-incr-stdev' );

var accumulator;
var v;
var i;

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

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

## Notice

This package is part of stdlib, a standard library for JavaScript and Node.js, with an emphasis on numerical and scientific computing. The library provides a collection of robust, high performance libraries for mathematics, statistics, streams, utilities, and more.

For more information on the project, filing bug reports and feature requests, and guidance on how to develop stdlib, see the main project repository.

## Package Sidebar

### Install

`npm i @stdlib/stats-incr-stdev`

### Repository

github.com/stdlib-js/stats-incr-stdev

stdlib.io

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0.2.2

Apache-2.0

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