Trying to solve symmetric difference using Javascr

Question

I am trying to figure out a solution for symmetric difference using javascript that accomplishes the following objectives:

• accepts an unspecified number of arrays as arguments
• preserves the original order of the numbers in the arrays
• does not remove duplicates of numbers in single arrays
• removes duplicates occurring across arrays

Thus, for example, if the input is ([1, 1, 2, 6], [2, 3, 5], [2, 3, 4]), the solution would be, [1, 1, 6, 5, 4].

I am trying to solve this as challenge given by an online coding community. The exact instructions of the challenge state,

Create a function that takes two or more arrays and returns an array of the symmetric difference of the provided arrays.

The mathematical term symmetric difference refers to the elements in two sets that are in either the first or second set, but not in both.

Although my solution below finds the numbers that are unique to each array, it eliminates all numbers occuring more than once and does not keep the order of the numbers.

My question is very close to the one asked at finding symmetric difference/unique elements in multiple arrays in javascript. However, the solution does not preserve the original order of the numbers and does not preserve duplicates of unique numbers occurring in single arrays.

function sym(args){
    var arr = [];
    var result = [];
    var units;
    var index = {};
    for(var i in arguments){
        units = arguments[i];

    for(var j = 0; j < units.length; j++){
         arr.push(units[j]);
        }
    }

    arr.forEach(function(a){
        if(!index[a]){
            index[a] = 0;
        }
            index[a]++;

    });

       for(var l in index){
           if(index[l] === 1){
               result.push(+l);
           }
       }

    return result;
}
symsym([1, 1, 2, 6], [2, 3, 5], [2, 3, 4]); // => Desired answer: [1, 1, 6. 5. 4]

Answer 1

function sym(arr1, arr2, ...rest) {

  //creating a array which has unique numbers from both the arrays
  const union = [...new Set([...arr1,...arr2])];

  // finding the Symmetric Difference between those two arrays
  const diff= union.filter((num)=>!(arr1.includes(num)&&arr2.includes(num)))

  //if there are more than 2 arrays
  if(rest.length){
    // recurrsively call till rest become 0 
    // i.e.  diff of 1,2 will be the first parameter so every recurrsive call will reduce     //  the arrays till diff between all of them are calculated.

    return sym(diff, rest[0], ...rest.slice(1))
  }
  return diff
}

Answer 2

Just use _.xor or copy lodash code.