npm package: @stdlib/stats-incr-mhmean
Description: Compute a moving harmonic mean incrementally.
Author: The Stdlib Authors
Latest version: 0.2.3

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# incrmhmean

[![NPM version][npm-image]][npm-url] [![Build Status][test-image]][test-url] [![Coverage Status][coverage-image]][coverage-url] <!-- [![dependencies][dependencies-image]][dependencies-url] -->

> Compute a moving [harmonic mean][harmonic-mean] incrementally.

<section class="intro">

The [harmonic mean][harmonic-mean] of positive real numbers `x_0, x_1, ..., x_{n-1}` is defined as

<!-- <equation class="equation" label="eq:harmonic_mean" align="center" raw="\begin{align}H &= \frac{n}{\frac{1}{x_0} + \frac{1}{x_1} + \cdots + \frac{1}{x_{n-1}}} \\ &= \frac{n}{\displaystyle\sum_{i=0}^{n-1} \frac{1}{x_i}} \\ &= \biggl( \frac{\displaystyle\sum_{i=0}^{n-1} \frac{1}{x_i}}{n} \biggr)^{-1}\end{align}" alt="Equation for the harmonic mean."> -->

<div class="equation" align="center" data-raw-text="\begin{align}H &amp;= \frac{n}{\frac{1}{x_0} + \frac{1}{x_1} + \cdots + \frac{1}{x_{n-1}}} \\ &amp;= \frac{n}{\displaystyle\sum_{i=0}^{n-1} \frac{1}{x_i}} \\ &amp;= \biggl( \frac{\displaystyle \sum_{i=0}^{n-1} \frac{1}{x_i}}{n} \biggr)^{-1}\end{align}" data-equation="eq:harmonic_mean">
    <img src="https://cdn.jsdelivr.net/gh/stdlib-js/stdlib@0a561712608b99b59d9243f7d478a2e2a019a130/lib/node_modules/@stdlib/stats/incr/mhmean/docs/img/equation_harmonic_mean.svg" alt="Equation for the harmonic mean.">
    <br>
</div>

<!-- </equation> -->

</section>

<!-- /.intro -->

<section class="installation">

## Installation

```bash
npm install @stdlib/stats-incr-mhmean
```

</section>

<section class="usage">

## Usage

```javascript
var incrmhmean = require( '@stdlib/stats-incr-mhmean' );
```

#### incrmhmean( window )

Returns an accumulator `function` which incrementally computes a moving [harmonic mean][harmonic-mean]. The `window` parameter defines the number of values over which to compute the moving [harmonic mean][harmonic-mean].

```javascript
var accumulator = incrmhmean( 3 );
```

#### accumulator( \[x] )

If provided an input value `x`, the accumulator function returns an updated [harmonic mean][harmonic-mean]. If not provided an input value `x`, the accumulator function returns the current [harmonic-mean][harmonic-mean].

```javascript
var accumulator = incrmhmean( 3 );

var v = accumulator();
// returns null

// Fill the window...
v = accumulator( 2.0 ); // [2.0]
// returns 2.0

v = accumulator( 1.0 ); // [2.0, 1.0]
// returns ~1.33

v = accumulator( 3.0 ); // [2.0, 1.0, 3.0]
// returns ~1.64

// Window begins sliding...
v = accumulator( 7.0 ); // [1.0, 3.0, 7.0]
// returns ~2.03

v = accumulator( 5.0 ); // [3.0, 7.0, 5.0]
// returns ~4.44

v = accumulator();
// returns ~4.44
```

</section>

<!-- /.usage -->

<section class="notes">

## 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 **at least** `W-1` 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.
-   As `W` values are needed to fill the window buffer, the first `W-1` returned values are calculated from smaller sample sizes. Until the window is full, each returned value is calculated from all provided values.

</section>

<!-- /.notes -->

<section class="examples">

## Examples

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

```javascript
var randu = require( '@stdlib/random-base-randu' );
var incrmhmean = require( '@stdlib/stats-incr-mhmean' );

var accumulator;
var v;
var i;

// Initialize an accumulator:
accumulator = incrmhmean( 5 );

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

</section>

<!-- /.examples -->

<!-- Section for related `stdlib` packages. Do not manually edit this section, as it is automatically populated. -->

<section class="related">

* * *

## See Also

-   <span class="package-name">[`@stdlib/stats-incr/hmean`][@stdlib/stats/incr/hmean]</span><span class="delimiter">: </span><span class="description">compute a harmonic mean incrementally.</span>
-   <span class="package-name">[`@stdlib/stats-incr/mgmean`][@stdlib/stats/incr/mgmean]</span><span class="delimiter">: </span><span class="description">compute a moving geometric mean incrementally.</span>
-   <span class="package-name">[`@stdlib/stats-incr/mmean`][@stdlib/stats/incr/mmean]</span><span class="delimiter">: </span><span class="description">compute a moving arithmetic mean incrementally.</span>

</section>

<!-- /.related -->

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<section class="main-repo" >

* * *

## Notice

This package is part of [stdlib][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][stdlib], see the main project [repository][stdlib].

#### Community

[![Chat][chat-image]][chat-url]

---

## License

See [LICENSE][stdlib-license].


## Copyright

Copyright &copy; 2016-2026. The Stdlib [Authors][stdlib-authors].

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[umd]: https://github.com/umdjs/umd
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[stdlib-license]: https://raw.githubusercontent.com/stdlib-js/stats-incr-mhmean/main/LICENSE

[harmonic-mean]: https://en.wikipedia.org/wiki/Harmonic_mean

<!-- <related-links> -->

[@stdlib/stats/incr/hmean]: https://www.npmjs.com/package/@stdlib/stats-incr-hmean

[@stdlib/stats/incr/mgmean]: https://www.npmjs.com/package/@stdlib/stats-incr-mgmean

[@stdlib/stats/incr/mmean]: https://www.npmjs.com/package/@stdlib/stats-incr-mmean

<!-- </related-links> -->

</section>

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