Cosine Distance

Computes the cosine distance between two arrays.

Cosine similarity defines vector similarity in terms of the angle separating two vectors.

The computed similarity resides on the interval [-1,1], where vectors with the same orientation have a similarity equal to 1, orthogonal orientation a similarity equal to 0, and opposite orientation a similarity equal to -1. The cosine distance seeks to express vector dissimilarity in positive space and does so by subtracting the similarity from 1.

Installation

$ npm install compute-cosine-distance

For use in the browser, use browserify.

Usage

var distance = require( 'compute-cosine-distance' );

distance( x, y[, accessor] )

Computes the cosine distance between two arrays.

var x = [ 5, 23, 2, 5, 9 ],
    y = [ 3, 21, 2, 5, 14 ];

var d = distance( x, y );
// returns ~0.025

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

var x = [
	{'x':2},
	{'x':4},
	{'x':5}
];

var y = [
	[1,3],
	[2,1],
	[3,5]
];

function getValue( d, i, j ) {
	if ( j === 0 ) {
		return d.x;
	}
	return d[ 1 ];
}

var d = distance( x, y, getValue );
// returns ~0.118

The accessor function is provided three arguments:

d: current datum.
i: current datum index.
j: array index; e.g., array x has index 0, and array y has index 1.

If provided empty arrays, the function returns null.

Examples

var distance = require( 'compute-cosine-distance' );

var x = new Array( 100 ),
	y = new Array( 100 ),
	d;

for ( var i = 0; i < x.length; i++ ) {
	x[ i ] = Math.round( Math.random()*100 );
	y[ i ] = Math.round( Math.random()*100 );
}
d = distance( x, y );

console.log( d );

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.

compute-io/cosine-distance