Symmetric Difference Challenge (DRY)!

JavaScript
1

This is my solution of Symmetric Difference Challenge!!!
How can i DRY (Don’t Repeat Yourself) the code?!
Thanks for advance

function sym(args) {
  var arr = Array.prototype.slice.call(arguments);
  
  function notNull(val) {
      return val !== null;
  }
  
  for(var x = 0; x < arr.length; x++) {
    for (var z = 1; z < arr[x].length; z++) {
      if(arr[x][z] == arr[x][z-1]) {
        delete arr[x][z-1];
      }
    }
    arr[x] = arr[x].filter(notNull);
  }
  
  while(arr.length > 1) {
    var temp = [];

    temp = arr.splice(0,1).concat(arr.splice(0,1));
    temp = temp.reduce(function(a, b) {
      return a.concat(b);
    });
    temp.sort();
    
    for(var i = 1; i < temp.length; i++) {
      if(temp[i] == temp[i-1]) {
        delete temp[i];
        delete temp[i-1];
      }
    }

    temp = temp.filter(notNull);
    arr.unshift(temp);
  }
  
  arr = arr.reduce(function(a, b) {
      return a.concat(b);
    });
  
  return arr;
}
2

When you find a chunk of code that is repeated, you can look at how to turn that into its own function or you can ask yourself if your function should be recursive.