Compare elements of two arrays

Question

I have two javascript array and I need to compare them. For example, suppose I have these two arrays:

var array1 = ["1", "2", "3", "4"];
var array2 = ["4", "1", "3", "2"];

These arrays are equal in fact and I want to get true as a result of comparison. What is the best and fastest way for doing that?

Answer 1

What you really have are two sets, not arrays, but unfortunately JavaScript does not provide any sort of "set" datatype. The easiest way to do this type of check is by using some sort of functional JavaScript library, such as lodash.

Using lodash's _.union function makes this trivially easy.

function setsEqual(a, b) {
  var u = _.union(a, b);
  return u.length === a.length && u.length === b.length;
}

---

If you want to do this without external libraries, you can do so using Array.prototype.every.

function setsEqual(a, b) {
  return a.length === b.length
      && a.every(function (v) { return b.indexOf(v) !== -1; });
}

Answer 2

The best way and fastest way to do this is using object which keep tracks the value of and its count. Then we can see if it exist in second array. Try this

function compare(arr1, arr2){
    var obj={}, len = arr1.length, i=0, isSame=true, prop;
    if(arr1.length === arr2.length){
        for(;i<len;i++){
            if(obj[arr1[i]]){
                obj[arr1[i]] = obj[arr1[i]]+1;
            } else{
                obj[arr1[i]] =1;
            }
        }
        i=0, len = arr2.length;
        for(;i<len;i++){
            if(obj[arr2[i]]){
                obj[arr2[i]] = obj[arr2[i]]-1;
            } else{
                isSame = false;
                break;
            }
        }
        for (prop in obj){
            if(obj[prop] > 0){
                isSame = false;
                break;
            }
        }
    }else{
        isSame = false;
    }
    return isSame;

}