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

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<details>
  <summary>
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# incrhmean

[![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 [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{\displaystyle n}{\displaystyle\sum_{i=0}^{n-1} \frac{1}{x_i}} \\ &= \biggl( \frac{\displaystyle\sum_{i=0}^{n-1} \frac{1}{x_i}}{\displaystyle 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{\displaystyle n}{\displaystyle\sum_{i=0}^{n-1} \frac{1}{x_i}} \\ &amp;= \biggl( \frac{\displaystyle\sum_{i=0}^{n-1} \frac{1}{x_i}}{\displaystyle n} \biggr)^{-1}\end{align}" data-equation="eq:harmonic_mean">
    <img src="https://cdn.jsdelivr.net/gh/stdlib-js/stdlib@2b632747053b9e357a4663369528fe62b29a6d55/lib/node_modules/@stdlib/stats/incr/hmean/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-hmean
```

</section>

<section class="usage">

## Usage

```javascript
var incrhmean = require( '@stdlib/stats-incr-hmean' );
```

#### incrhmean()

Returns an accumulator `function` which incrementally computes a [harmonic mean][harmonic-mean].

```javascript
var accumulator = incrhmean();
```

#### 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 = incrhmean();

var v = accumulator( 2.0 );
// returns 2.0

v = accumulator( 1.0 );
// returns ~1.33

v = accumulator( 3.0 );
// returns ~1.64

v = accumulator();
// returns ~1.64
```

</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 **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.

</section>

<!-- /.notes -->

<section class="examples">

## Examples

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

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

var accumulator;
var v;
var i;

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

// For each simulated datum, update the 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/gmean`][@stdlib/stats/incr/gmean]</span><span class="delimiter">: </span><span class="description">compute a geometric mean incrementally.</span>
-   <span class="package-name">[`@stdlib/stats-incr/mean`][@stdlib/stats/incr/mean]</span><span class="delimiter">: </span><span class="description">compute an arithmetic mean incrementally.</span>
-   <span class="package-name">[`@stdlib/stats-incr/mhmean`][@stdlib/stats/incr/mhmean]</span><span class="delimiter">: </span><span class="description">compute a moving harmonic mean incrementally.</span>
-   <span class="package-name">[`@stdlib/stats-incr/summary`][@stdlib/stats/incr/summary]</span><span class="delimiter">: </span><span class="description">compute a statistical summary 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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[stdlib]: https://github.com/stdlib-js/stdlib

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

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

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

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

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

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

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

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</section>

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