// wink-distance
// Distance functions for Bag of Words, Strings,
// Vectors and more.
//
// Copyright (C) GRAYPE Systems Private Limited
//
// This file is part of “wink-distance”.
//
// Permission is hereby granted, free of charge, to any person obtaining a
// copy of this software and associated documentation files (the "Software"),
// to deal in the Software without restriction, including without limitation
// the rights to use, copy, modify, merge, publish, distribute, sublicense,
// and/or sell copies of the Software, and to permit persons to whom the
// Software is furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included
// in all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
// THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
// DEALINGS IN THE SOFTWARE.
//
// Because we want to logically group the variables.
/* eslint sort-vars: 0 */
// ## bow
// ### cosine
/**
*
* Computes the cosine distance between the input bag of words (bow)
* `a` and `b` and returns a value between 0 and 1.
*
* @method bow.cosine
* @param {object} a the first set of bows i.e word (i.e. key) and it's frequency
* (i.e. value) pairs.
* @param {object} b the second set of bows.
* @return {number} cosine distance between `a` and `b`.
*
* @example
* // bow for "the dog chased the cat"
* var a = { the: 2, dog: 1, chased: 1, cat: 1 };
* // bow for "the cat chased the mouse"
* var b = { the: 2, cat: 1, chased: 1, mouse: 1 };
* cosine( a, b );
* // -> 0.14285714285714302
* // Note the bow could have been created directly by
* // using "tokens.bow()" from the "wink-nlp-utils".
*/
var cosine = function ( a, b ) {
// `ab` & `ba` additional variables are required as you dont want to corrupt
// `a` & `b`!
// Updated `a` with words in `b` set as 0 in `a`.
var ab = Object.create( null );
// Updated `b` with words in `a` set as 0 in `b`.
var ba = Object.create( null );
var distance;
var w; // a word!
// Fill up `ab` and `ba`
for ( w in a ) { // eslint-disable-line guard-for-in
ab[ w ] = a[ w ];
ba[ w ] = 0;
}
for ( w in b ) { // eslint-disable-line guard-for-in
ba[ w ] = b[ w ];
ab[ w ] = ab[ w ] || 0;
}
// With `ab` & `ba` in hand, its easy to transform in to
// vector: its a frequency of each word found in both strings
// We do not need to store these vectors in arrays, instead we can perform
// processing in the same loop.
var sa2 = 0, // sum of ai^2
saxb = 0, // sum of ai x bi
sb2 = 0, // sum of bi^2
va, vb; // value of ai and bi
// One could have used `ba`, as both have same words now!
for ( w in ab ) { // eslint-disable-line guard-for-in
va = ab[ w ];
vb = ba[ w ];
sa2 += va * va;
sb2 += vb * vb;
saxb += va * vb;
}
// Compute cosine distance; ensure you dont get `NaN i.e. 0/0` by testing for
// `sa2` and `sb2`.
distance = 1 - (
( sa2 && sb2 ) ?
// Compute cosine if both of them are non-zero.
( saxb / ( Math.sqrt( sa2 ) * Math.sqrt( sb2 ) ) ) :
// If one of them is 0 means **0 distance** otherwise a distance of **1**.
( !sa2 ^ !sb2 ) ? 0 : 1 // eslint-disable-line no-bitwise
);
return distance;
}; // cosine()
// Export cosine
module.exports = cosine;
