compute-median/README.md

Computes the median of an array.

Median
===
[![NPM version][npm-image]][npm-url] [![Build Status][travis-image]][travis-url] [![Coverage Status][coveralls-image]][coveralls-url] [![Dependencies][dependencies-image]][dependencies-url]

> Computes the [median](http://en.wikipedia.org/wiki/Median) of an array.


## Installation

``` bash
$ npm install compute-median
```

For use in the browser, use [browserify](https://github.com/substack/node-browserify).


## Usage

``` javascript
var median = require( 'compute-median' );
```

#### median( arr[, options] )

Computes the median of an `array`. For unsorted primitive number `arrays`,

``` javascript
var unsorted = [ 5, 3, 2, 4 ];

var m1 = median( unsorted );
// returns 3.5
```

The function accepts two `options`:

*	`sorted`: `boolean` flag indicating if the input `array` is sorted in __ascending__ order. Default: `false`.
*	`accessor`: accessor `function` for accessing values in object `arrays`.

If the input `array` is already sorted in __ascending__ order, set the `sorted` option to `true`.

``` javascript
var sorted = [ 2, 3, 4, 5 ];

var m2 = median( sorted, {
	'sorted': true,
});
// returns 3.5
```

For object `arrays`, provide an accessor `function` for accessing numeric `array` values

``` javascript
var data = [
	[1,5],
	[3,3],
	[4,2],
	[5,4],
];

function getValue( d ) {
	return d[ 1 ];
}

var m3 = median( data, {
	'sorted': false,
	'accessor': getValue
});
// returns 3.5
```

__Note__: if provided an empty `array`, the function returns `null`.


## Examples

``` javascript
var median = require( 'compute-median' );

var data = new Array( 1001 );
for ( var i = 0; i < data.length; i++ ) {
	data[ i ] = Math.round( Math.random() * 100 );
}
console.log( median( data ) );
```

To run the example code from the top-level application directory,

``` bash
$ node ./examples/index.js
```


## Notes

For an input `array` of length `N`,

*	if provided a sorted (in __ascending__ order) numeric `array`, the function is `O(1)`.
*	if provided a sorted object `array`, the function is `O(N)`.
*	if provided an unsorted numeric `array`, the function is `O( N log(N) )`.
* 	if provided an unsorted object `array`, the function is `O( N + N log(N) )`.


## Tests

### Unit

Unit tests use the [Mocha](http://mochajs.org) test framework with [Chai](http://chaijs.com) assertions. To run the tests, execute the following command in the top-level application directory:

``` bash
$ make test
```

All new feature development should have corresponding unit tests to validate correct functionality.


### Test Coverage

This repository uses [Istanbul](https://github.com/gotwarlost/istanbul) as its code coverage tool. To generate a test coverage report, execute the following command in the top-level application directory:

``` bash
$ make test-cov
```

Istanbul creates a `./reports/coverage` directory. To access an HTML version of the report,

``` bash
$ make view-cov
```


---
## License

[MIT license](http://opensource.org/licenses/MIT).


## Copyright

Copyright &copy; 2014-2015. Athan Reines.


[npm-image]: http://img.shields.io/npm/v/compute-median.svg
[npm-url]: https://npmjs.org/package/compute-median

[travis-image]: http://img.shields.io/travis/compute-io/median/master.svg
[travis-url]: https://travis-ci.org/compute-io/median

[coveralls-image]: https://img.shields.io/coveralls/compute-io/median/master.svg
[coveralls-url]: https://coveralls.io/r/compute-io/median?branch=master

[dependencies-image]: http://img.shields.io/david/compute-io/median.svg
[dependencies-url]: https://david-dm.org/compute-io/median

[dev-dependencies-image]: http://img.shields.io/david/dev/compute-io/median.svg
[dev-dependencies-url]: https://david-dm.org/dev/compute-io/median

[github-issues-image]: http://img.shields.io/github/issues/compute-io/median.svg
[github-issues-url]: https://github.com/compute-io/median/issues