Calculate the Intersection of Arrays

readme.md

Array intersect

Fastest function to intersect a large number of big arrays in javascript, without dependencies

• The compressed version is only 345 caracters long.
• Faster than common libraries, even a large number of arrays, or on very big arrays. (See benchmarks)

Usage

array_intersect(array1, array2, ..., arrayN)

How it works

[ Credits to https://gist.github.com/lovasoa/3361645 ]

The idea is simple and comes from here: http://pioupioum.fr/developpement/javascript-array-intersection.html.

To make short story even shorter: It creates a javascript object, the keys of which are the elements of the smallest of the arrays we want to intersect.

A comparision for all array intersections - https://codeburst.io/optimizing-array-analytics-in-javascript-part-two-search-intersection-and-cross-products-79b4a6d68da0

array_intersect.min.js

function array_intersect(){var a,b,c,d,e,f,g=[],h={},i;i=arguments.length-1;d=arguments[0].length;c=0;for(a=0;a<=i;a++){e=arguments[a].length;if(e<d){c=a;d=e}}for(a=0;a<=i;a++){e=a===c?0:a||c;f=arguments[e].length;for(var j=0;j<f;j++){var k=arguments[e][j];if(h[k]===a-1){if(a===i){g.push(k);h[k]=0}else{h[k]=a}}else if(a===0){h[k]=0}}}return g}

array_intersection.js

function array_intersect() {
  var i, all, shortest, nShortest, n, len, ret = [], obj={}, nOthers;
  nOthers = arguments.length-1;
  nShortest = arguments[0].length;
  shortest = 0;
  for (i=0; i<=nOthers; i++){
    n = arguments[i].length;
    if (n<nShortest) {
      shortest = i;
      nShortest = n;
    }
  }

  for (i=0; i<=nOthers; i++) {
    n = (i===shortest)?0:(i||shortest); //Read the shortest array first. Read the first array instead of the shortest
    len = arguments[n].length;
    for (var j=0; j<len; j++) {
        var elem = arguments[n][j];
        if(obj[elem] === i-1) {
          if(i === nOthers) {
            ret.push(elem);
            obj[elem]=0;
          } else {
            obj[elem]=i;
          }
        }else if (i===0) {
          obj[elem]=0;
        }
    }
  }
  return ret;
}