jaccard-array/jaccard.js

Very simple package for measuring the similarity of two sets by their shared members.

module.exports =  function(arrayA, arrayB){
  if (Array.isArray(arrayA) && Array.isArray(arrayB)) {
    // create sets from arrays to ensure unique values
    let setA = new Set(arrayA);
    let setB = new Set(arrayB);

    let intersection = countIntersection(setA, setB);
    let union = countUnion(setA, setB);

    return getJaccardIndex(intersection, union);
  } else {
    throw 'Parameter(s) should be of type Array.';
  }
}

function countIntersection(setA, setB) {
  let refArray = [...setA];
   // iterate over setA as an array
   // return 1/0 for every element in/not in setB
   // return the sum
   return refArray
             .map(elem => setB.has(elem) ? 1 : 0)
             .reduce((culminative, current) => culminative+current );
}

function countUnion(setA, setB){
  //create a new set of unique elements from A and B
  let union = new Set([...setA, ...setB]);
  // return its size
  return union.size;
}

function getJaccardIndex(intersection, union) {
  return  intersection / union;
}