npm package: @stdlib/stats-iter-msum
Description: Create an iterator which iteratively computes a moving sum.
Author: The Stdlib Authors
Latest version: 0.2.3

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  <summary>
    About stdlib...
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# itermsum

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

> Create an [iterator][mdn-iterator-protocol] which iteratively computes a moving sum.

<section class="intro">

For a window of size `W`, the moving sum is defined as

<!-- <equation class="equation" label="eq:moving_sum" align="center" raw="s = \sum_{i=0}^{W-1} x_i" alt="Equation for the moving sum."> -->

<div class="equation" align="center" data-raw-text="s = \sum_{i=0}^{W-1} x_i" data-equation="eq:moving_sum">
    <img src="https://cdn.jsdelivr.net/gh/stdlib-js/stdlib@649f1d940ae76f02c3c2fc97e52f59b452e2e15f/lib/node_modules/@stdlib/stats/iter/msum/docs/img/equation_moving_sum.svg" alt="Equation for the moving sum.">
    <br>
</div>

<!-- </equation> -->

</section>

<!-- /.intro -->

<!-- Package usage documentation. -->

<section class="installation">

## Installation

```bash
npm install @stdlib/stats-iter-msum
```

</section>

<section class="usage">

## Usage

```javascript
var itermsum = require( '@stdlib/stats-iter-msum' );
```

#### itermsum( iterator, W )

Returns an [iterator][mdn-iterator-protocol] which iteratively computes a moving sum. The `W` parameter defines the number of iterated values over which to compute the moving sum.

```javascript
var array2iterator = require( '@stdlib/array-to-iterator' );

var arr = array2iterator( [ 2.0, 1.0, 3.0, -7.0, -5.0 ] );
var it = itermsum( arr, 3 );

// Fill the window...
var s = it.next().value; // [2.0]
// returns 2.0

s = it.next().value; // [2.0, 1.0]
// returns 3.0

s = it.next().value; // [2.0, 1.0, 3.0]
// returns 6.0

// Window begins sliding...
s = it.next().value; // [1.0, 3.0, -7.0]
// returns -3.0

s = it.next().value; // [3.0, -7.0, -5.0]
// returns -9.0
```

</section>

<!-- /.usage -->

<!-- Package usage notes. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->

<section class="notes">

## Notes

-   If an iterated value is non-numeric (including `NaN`), the function returns `NaN` for **at least** `W-1` future invocations. If non-numeric iterated values are possible, you are advised to provide an [`iterator`][mdn-iterator-protocol] which type checks and handles non-numeric values accordingly.
-   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 previously iterated values.

</section>

<!-- /.notes -->

<!-- Package usage examples. -->

<section class="examples">

## Examples

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

```javascript
var runif = require( '@stdlib/random-iter-uniform' );
var itermsum = require( '@stdlib/stats-iter-msum' );

// Create an iterator for generating uniformly distributed pseudorandom numbers:
var rand = runif( -10.0, 10.0, {
    'seed': 1234,
    'iter': 100
});

// Create an iterator for iteratively computing a moving sum:
var it = itermsum( rand, 3 );

// Perform manual iteration...
var v;
while ( true ) {
    v = it.next();
    if ( v.done ) {
        break;
    }
    if ( typeof v.value === 'number' ) {
        console.log( 'sum: %d', v.value );
    }
}
```

</section>

<!-- /.examples -->

<!-- Section to include cited references. If references are included, add a horizontal rule *before* the section. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->

<section class="references">

</section>

<!-- /.references -->

<!-- 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-iter/mmean`][@stdlib/stats/iter/mmean]</span><span class="delimiter">: </span><span class="description">create an iterator which iteratively computes a moving arithmetic mean.</span>
-   <span class="package-name">[`@stdlib/stats-iter/sum`][@stdlib/stats/iter/sum]</span><span class="delimiter">: </span><span class="description">compute the sum of all iterated values.</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].

</section>

<!-- /.stdlib -->

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[umd]: https://github.com/umdjs/umd
[es-module]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Modules

[deno-url]: https://github.com/stdlib-js/stats-iter-msum/tree/deno
[deno-readme]: https://github.com/stdlib-js/stats-iter-msum/blob/deno/README.md
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[branches-url]: https://github.com/stdlib-js/stats-iter-msum/blob/main/branches.md

[stdlib-license]: https://raw.githubusercontent.com/stdlib-js/stats-iter-msum/main/LICENSE

[mdn-iterator-protocol]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols#The_iterator_protocol

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

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

[@stdlib/stats/iter/sum]: https://www.npmjs.com/package/@stdlib/stats-iter-sum

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

</section>

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