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# Median

Computes the median of an array.

## Installation

``````\$ npm install compute-median
``````

For use in the browser, use browserify.

## Usage

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

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

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

``````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`.

``````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

``````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

``````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,

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

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 test framework with Chai assertions. To run the tests, execute the following command in the top-level application directory:

``````\$ make test
``````

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

### Test Coverage

This repository uses Istanbul as its code coverage tool. To generate a test coverage report, execute the following command in the top-level application directory:

``````\$ make test-cov
``````

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

``````\$ make view-cov
``````

## Rate & Review

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