# compute-quantile

Computes a quantile for a numeric array.

## Stats

StarsIssuesVersionUpdatedCreatedSize
compute-quantile
1.0.18 years ago8 years ago Quantile
!NPM versionnpm-imagenpm-url !Build Statustravis-imagetravis-url !Coverage Statuscoveralls-imagecoveralls-url !Dependenciesdependencies-imagedependencies-url
Computes a quantile for a numeric array.

This module determines the nearest rank and returns the `array` value corresponding to that rank.
This module does not currently support multiple interpolation methods, and instead uses a standard elementary method for estimating the quantile.

## Installation

``\$ npm install compute-quantile``

For use in the browser, use browserify.

## Usage

To use the module,
``var quantile = require( 'compute-quantile' );``

#### quantile( arr, p, opts )

Given a probability `0 <= p <= 1`, computes the quantile for an input `array`.
``````var unsorted = [ 4, 3, 5, 1, 2 ];

var q = quantile( unsorted, 0.25 );
// returns 2``````

If the input `array` is already sorted in ascending order, you can set the `sorted` option to `true`.
``````var sorted = [ 1, 2, 3, 4, 5 ];

var q = quantile( sorted, 0.25, { 'sorted': true } );
// returns 2``````

## Examples

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

// Simulate some data...
var data = new Array( 1000 );

for ( var i = 0, len = data.length; i < len; i++ ) {
data[ i ] = Math.round( Math.random()*1000 );
}

// Compute the p-quantile for p = 0.5 (median):
console.log( quantile( data, 0.5 ) );``````

To run the example code from the top-level application directory,
``\$ node ./examples/index.js``

## Notes

The probability `p` is equal to `k / q`, where `q` is the total number of quantiles and `k` is the k th quantile.
If the input `array` is not sorted in ascending order, the function is `O( N log(N) )`, where `N` is the input `array` length. If the `array` is sorted, the function is `O(1)`.

## 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``