code: function uniqBy(array, iteratee) {
    return (array && array.length)
      ? baseUniq(array, baseIteratee(iteratee, 2))
      : [];
  }
docs: This method is like `_.uniq` except that it accepts `iteratee` which is
  invoked for each element in `array` to generate the criterion by which
  uniqueness is computed. The order of result values is determined by the
  order they occur in the array. The iteratee is invoked with one argument:
  (value).
  
  @static
  @memberOf _
  @since 4.0.0
  @category Array
  @param {Array} array The array to inspect.
  @param {Function} [iteratee=_.identity]
  The iteratee invoked per element.
  @returns {Array} Returns the new duplicate free array.
  @example
  
  _.uniqBy([2.1, 1.2, 2.3], Math.floor);
  // => [2.1, 1.2]
  
  // The `_.property` iteratee shorthand.
  _.uniqBy([{ 'x': 1 }, { 'x': 2 }, { 'x': 1 }], 'x');
  // => [{ 'x': 1 }, { 'x': 2 }]