Orignal solution to _.sortedIndex

  _.sortedIndex = function(array, obj, iteratee, context) {
    iteratee = cb(iteratee, context, 1);
    var value = iteratee(obj) === undefined ? Infinity : iteratee(obj);
    var low = 0, high = array.length;
    while (low < high) {
      var mid = Math.floor((low + high) / 2);
      if (iteratee(array[mid]) <= value) low = mid + 1; else high = mid;
    }
    return low;
  };