fuzzy-string-matching-using-cosine-similarity

fuzzy.js

// http://blog.nishtahir.com/2015/09/19/fuzzy-string-matching-using-cosine-similarity/

'use strict';

Set.intersection = function*( set1, set2 )
{
    for ( let value of set1.values() )
    {
        if ( set2.has( value ) )
        {
            yield value;
        }
    }
};

const getTermFrequencyMap = ( terms ) =>
{
    const map = new Map();
    
    for ( let term of terms )
    {
        const n = map.get( term );
        
        if ( n === undefined )
        { 
            map.set( term, 1 ); 
        }
        else 
        { 
            map.set( term, n + 1 );
        }
    }
    
    return map;
};

const cosineSimilarity = (text1, text2) =>
{
    const a = getTermFrequencyMap(text1);
    const b = getTermFrequencyMap(text2);

    const s1 = new Set(a.keys());
    const s2 = new Set(b.keys());
 
    let dotProduct = 0;
    let magnitudeA = 0;
    let magnitudeB = 0;
    
    for ( let item of Set.intersection( s1, s2 ) )
    {
        dotProduct += a.get( item ) * b.get( item );
    }
  
    for ( let k of a.keys() )
    {
        magnitudeA += Math.pow( a.get( k ), 2 );
    }
  
  for ( let k of b.keys() )
  {
     magnitudeB += Math.pow( b.get( k ), 2 );
  }

  return dotProduct / Math.sqrt( magnitudeA * magnitudeB );
};