JavaScript: Eliminating Elements From Array Via Passed Arguments

Question

Working on a challenge from freeCodeCamp, where I have to create a function that takes in an array and a number of other arguments. If an element within the passed array matches one of the passed arguments, it has to be removed from the array.

I have written this code, but it does not work for all of the tests:

function destroyer(arr) {

  var args = Array.prototype.slice.call(arguments);

  for(i=0; i<arr.length; i++){
    for(var j=0; j<args.length; j++){
      if(args[j]===arr[i]){
        arr.splice(i,1); 
      }
    }
  }  
  return arr;
}

destroyer([1, 2, 3, 1, 2, 3], 2, 3);

Step 1: Convert arguments object into an array, so I can treat it like one. Step 2: Run nested for-loop to find any matches between the passed array and the passed array of arguments. Step 3: If a match is found, eliminate it using .splice(i,1).

Shouldn't that do the trick? What am I doing wrong?

EDIT: This is an example of a test that it fails:

destroyer([3, 5, 1, 2, 2], 2, 3, 5) should return [1].

maybe give an example of a failing test ?

JohnPan
– JohnPan

2017-06-29 07:42:19 +00:00
Commented Jun 29, 2017 at 7:42 — JohnPan
– JohnPan, Commented Jun 29, 2017 at 7:42

Yury Tarabanko · Accepted Answer · 2017-06-29 07:56:46Z

4

You are changing array while iterating over it. So after the first splice indices change.

You could use filter and indexOf to do this.

function destroyer(array) {
  var toRemove = [].slice.call(arguments, 1);
  
  return array.filter(function(item) {
    return toRemove.indexOf(item) === -1
  })
}

console.log(destroyer([3, 5, 1, 2, 2], 2, 3, 5))

If you still want to use for-loop. But keep in mind that splice mutates array. So your function does mutate arguments which should usually be avoided.

function destroyer(arr) {

  var args = Array.prototype.slice.call(arguments);

  for(var i=0; i<arr.length; i++){
    for(var j=1; j<args.length; j++){
      if(args[j]===arr[i]){
        arr.splice(i,1);
        i--; // manually reduce index
      }
    }
  }  
  return arr;
}

console.log(destroyer([1, 2, 3, 1, 2, 3], 2, 3));
console.log(destroyer([3, 5, 1, 2, 2], 2, 3, 5));

edited Jun 29, 2017 at 7:56

answered Jun 29, 2017 at 7:49

Yury Tarabanko

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Comments

Lennholm · Accepted Answer · 2017-06-29 08:00:43Z

The problem is that every time you remove an item from arr, your loop will skip the next item. Imagine you're iterating over the following array:

['a', 'b', 'c', 'd', 'e']

Say you're at iteration 2, corresponding to the 'c' item in the array and you remove that item. Your array will now look like this:

['a', 'b', 'd', 'e']

Now 'd' will correspond to the current iteration 2 but your for lopp will continue on with the next iteration, 3, and the 'd' item will never be processed.

Since the array is being modified, I would suggest using a while loop instead:

var i = 0;
while (i < arr.length){
  for(var j=0; j<args.length; j++){
    if(args[j]===arr[i]){
      arr.splice(i,1); 
    } else {
      i++;
    }
  }
}

Here, i is not incremented if you removed the item since that meant the next item was moved to the current position of i

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