nanquantiles

Computes quantiles for an array ignoring non-numeric values.

Installation

$ npm install compute-nanquantiles

For use in the browser, use browserify.

Usage

var nanquantiles = require( 'compute-nanquantiles' );

nanquantiles( arr, num[, opts] )

Computes q-quantiles for an array ignoring non-numeric values. num specifies the number of quantiles to compute. For unsorted primitive arrays,

var unsorted = [ 4, 2, null, 5, 3 ];

var q = nanquantiles( unsorted, 2 );
// returns [ 2, 3.5, 5 ]

The function accepts the following options:

• sorted: boolean flag indicating if an input array is sorted in ascending order. Default: false.
• accessor: accessor function for accessing values in an object array.

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

var sorted = [ 2, 3, null, 4, 5 ];

var q = nanquantiles( sorted, 2, {
	'sorted': true
});
// returns [ 2, 3.5, 5 ];

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

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

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

var q = nanquantiles( data, 2, {
	'sorted': true,
	'accessor': getValue
});
// returns [ 2, 3.5, 5 ];

Notes

• For an input array containing no numeric values, the function returns null.
• The function returns the 0th and 100th quantiles; a.k.a., the min and the max. For example, when computing the median,

var data = new Array( 11 );

for ( var i = 0; i < data.length; i++ ) {
	data[ i ] = i + 1;
}
console.log( nanquantiles( data, 2 ) );
// returns [ 1, 6, 11 ]

the function returns [1,6,11], where min = 1, max = 11, and median = 6. Accordingly, you should expect the output to be an array with length = q + 1, where q is the number of quantiles.

Examples

var nanquantiles = require( 'compute-nanquantiles' );

var data = new Array( 1000 );
for ( var i = 0; i < data.length; i++ ) {
	if ( i%2 === 0 ) {
		data[ i ] = null;
	} else {
		data[ i ] = Math.round( Math.random() * 100 );
	}
}
console.log( nanquantiles( data, 10 ) );

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

$ node ./examples/index.js

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

License

MIT license.

Copyright

Copyright © 2015. Philipp Burckhardt.