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https://github.com/stdlib-js/stats-base-meanors

Calculate the arithmetic mean of a strided array using ordinary recursive summation.
https://github.com/stdlib-js/stats-base-meanors

arithmetic-mean array average avg central-tendency javascript math mathematics mean node node-js nodejs ors statistics stats stdlib strided strided-array

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Calculate the arithmetic mean of a strided array using ordinary recursive summation.

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README 

        



  

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# meanors



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



> Calculate the [arithmetic mean][arithmetic-mean] of a strided array using ordinary recursive summation.



The [arithmetic mean][arithmetic-mean] is defined as



```math

\mu = \frac{1}{n} \sum_{i=0}^{n-1} x_i

```



## Installation



```bash

npm install @stdlib/stats-base-meanors

```



Alternatively,



-   To load the package in a website via a `script` tag without installation and bundlers, use the [ES Module][es-module] available on the [`esm`][esm-url] branch (see [README][esm-readme]).

-   If you are using Deno, visit the [`deno`][deno-url] branch (see [README][deno-readme] for usage intructions).

-   For use in Observable, or in browser/node environments, use the [Universal Module Definition (UMD)][umd] build available on the [`umd`][umd-url] branch (see [README][umd-readme]).



The [branches.md][branches-url] file summarizes the available branches and displays a diagram illustrating their relationships.



To view installation and usage instructions specific to each branch build, be sure to explicitly navigate to the respective README files on each branch, as linked to above.



## Usage



```javascript

var meanors = require( '@stdlib/stats-base-meanors' );

```



#### meanors( N, x, stride )



Computes the [arithmetic mean][arithmetic-mean] of a strided array `x` using ordinary recursive summation.



```javascript

var x = [ 1.0, -2.0, 2.0 ];

var N = x.length;



var v = meanors( N, x, 1 );

// returns ~0.3333

```



The function has the following parameters:



-   **N**: number of indexed elements.

-   **x**: input [`Array`][mdn-array] or [`typed array`][mdn-typed-array].

-   **stride**: index increment for `x`.



The `N` and `stride` parameters determine which elements in `x` are accessed at runtime. For example, to compute the [arithmetic mean][arithmetic-mean] of every other element in `x`,



```javascript

var floor = require( '@stdlib/math-base-special-floor' );



var x = [ 1.0, 2.0, 2.0, -7.0, -2.0, 3.0, 4.0, 2.0 ];

var N = floor( x.length / 2 );



var v = meanors( N, x, 2 );

// returns 1.25

```



Note that indexing is relative to the first index. To introduce an offset, use [`typed array`][mdn-typed-array] views.



```javascript

var Float64Array = require( '@stdlib/array-float64' );

var floor = require( '@stdlib/math-base-special-floor' );



var x0 = new Float64Array( [ 2.0, 1.0, 2.0, -2.0, -2.0, 2.0, 3.0, 4.0 ] );

var x1 = new Float64Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element



var N = floor( x0.length / 2 );



var v = meanors( N, x1, 2 );

// returns 1.25

```



#### meanors.ndarray( N, x, stride, offset )



Computes the [arithmetic mean][arithmetic-mean] of a strided array using ordinary recursive summation and alternative indexing semantics.



```javascript

var x = [ 1.0, -2.0, 2.0 ];

var N = x.length;



var v = meanors.ndarray( N, x, 1, 0 );

// returns ~0.33333

```



The function has the following additional parameters:



-   **offset**: starting index for `x`.



While [`typed array`][mdn-typed-array] views mandate a view offset based on the underlying `buffer`, the `offset` parameter supports indexing semantics based on a starting index. For example, to calculate the [arithmetic mean][arithmetic-mean] for every other value in `x` starting from the second value



```javascript

var floor = require( '@stdlib/math-base-special-floor' );



var x = [ 2.0, 1.0, 2.0, -2.0, -2.0, 2.0, 3.0, 4.0 ];

var N = floor( x.length / 2 );



var v = meanors.ndarray( N, x, 2, 1 );

// returns 1.25

```



## Notes



-   If `N <= 0`, both functions return `NaN`.

-   Ordinary recursive summation (i.e., a "simple" sum) is performant, but can incur significant numerical error. If performance is paramount and error tolerated, using ordinary recursive summation to compute an arithmetic mean is acceptable; in all other cases, exercise due caution.

-   Depending on the environment, the typed versions ([`dmeanors`][@stdlib/stats/base/dmeanors], [`smeanors`][@stdlib/stats/base/smeanors], etc.) are likely to be significantly more performant.



## Examples



```javascript

var randu = require( '@stdlib/random-base-randu' );

var round = require( '@stdlib/math-base-special-round' );

var Float64Array = require( '@stdlib/array-float64' );

var meanors = require( '@stdlib/stats-base-meanors' );



var x;

var i;



x = new Float64Array( 10 );

for ( i = 0; i < x.length; i++ ) {

    x[ i ] = round( (randu()*100.0) - 50.0 );

}

console.log( x );



var v = meanors( x.length, x, 1 );

console.log( v );

```



* * *



## See Also



-   [`@stdlib/stats-base/dmeanors`][@stdlib/stats/base/dmeanors]: calculate the arithmetic mean of a double-precision floating-point strided array using ordinary recursive summation.

-   [`@stdlib/stats-base/mean`][@stdlib/stats/base/mean]: calculate the arithmetic mean of a strided array.

-   [`@stdlib/stats-base/nanmeanors`][@stdlib/stats/base/nanmeanors]: calculate the arithmetic mean of a strided array, ignoring NaN values and using ordinary recursive summation.

-   [`@stdlib/stats-base/smeanors`][@stdlib/stats/base/smeanors]: calculate the arithmetic mean of a single-precision floating-point strided array using ordinary recursive summation.



* * *



## 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 © 2016-2024. The Stdlib [Authors][stdlib-authors].



[npm-image]: http://img.shields.io/npm/v/@stdlib/stats-base-meanors.svg

[npm-url]: https://npmjs.org/package/@stdlib/stats-base-meanors



[test-image]: https://github.com/stdlib-js/stats-base-meanors/actions/workflows/test.yml/badge.svg?branch=main

[test-url]: https://github.com/stdlib-js/stats-base-meanors/actions/workflows/test.yml?query=branch:main



[coverage-image]: https://img.shields.io/codecov/c/github/stdlib-js/stats-base-meanors/main.svg

[coverage-url]: https://codecov.io/github/stdlib-js/stats-base-meanors?branch=main



[chat-image]: https://img.shields.io/gitter/room/stdlib-js/stdlib.svg

[chat-url]: https://app.gitter.im/#/room/#stdlib-js_stdlib:gitter.im



[stdlib]: https://github.com/stdlib-js/stdlib



[stdlib-authors]: https://github.com/stdlib-js/stdlib/graphs/contributors



[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-base-meanors/tree/deno

[deno-readme]: https://github.com/stdlib-js/stats-base-meanors/blob/deno/README.md

[umd-url]: https://github.com/stdlib-js/stats-base-meanors/tree/umd

[umd-readme]: https://github.com/stdlib-js/stats-base-meanors/blob/umd/README.md

[esm-url]: https://github.com/stdlib-js/stats-base-meanors/tree/esm

[esm-readme]: https://github.com/stdlib-js/stats-base-meanors/blob/esm/README.md

[branches-url]: https://github.com/stdlib-js/stats-base-meanors/blob/main/branches.md



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



[arithmetic-mean]: https://en.wikipedia.org/wiki/Arithmetic_mean



[mdn-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array



[mdn-typed-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray



[@stdlib/stats/base/dmeanors]: https://github.com/stdlib-js/stats-base-dmeanors



[@stdlib/stats/base/mean]: https://github.com/stdlib-js/stats-base-mean



[@stdlib/stats/base/nanmeanors]: https://github.com/stdlib-js/stats-base-nanmeanors



[@stdlib/stats/base/smeanors]: https://github.com/stdlib-js/stats-base-smeanors