Optimizing removal of elements at positions, when list of positions is greater than 100,000 and array is >250,000.

gistfile1.js

function filterOutPositions(array, positions) @param -- positions to remove
  {
    var BE_DELETED = {};

    var arr = array.slice(0); // Clone the array so it can be re-used (non-destructive)
    var pos_len = positions.length;
    for (var i=0; i < pos_len; i++)
    {
      arr[ positions[i] ] = BE_DELETED;
    }

    // Finally, delete the marked positions
    for (var ii=arr.length-1; ii >= 0; ii--)
    {
      if ( arr[ii] === BE_DELETED )
      {
        arr.splice(ii, 1);
      }
    }
    return arr;
  }