1  var baseFlatten = require('./_baseFlatten'),
 2      baseIteratee = require('./_baseIteratee'),
 3      baseRest = require('./_baseRest'),
 4      baseUniq = require('./_baseUniq'),
 5      isArrayLikeObject = require('./isArrayLikeObject'),
 6      last = require('./last');
 7  
 8  /**
 9   * This method is like `_.union` except that it accepts `iteratee` which is
10   * invoked for each element of each `arrays` to generate the criterion by
11   * which uniqueness is computed. Result values are chosen from the first
12   * array in which the value occurs. The iteratee is invoked with one argument:
13   * (value).
14   *
15   * @static
16   * @memberOf _
17   * @since 4.0.0
18   * @category Array
19   * @param {...Array} [arrays] The arrays to inspect.
20   * @param {Function} [iteratee=_.identity] The iteratee invoked per element.
21   * @returns {Array} Returns the new array of combined values.
22   * @example
23   *
24   * _.unionBy([2.1], [1.2, 2.3], Math.floor);
25   * // => [2.1, 1.2]
26   *
27   * // The `_.property` iteratee shorthand.
28   * _.unionBy([{ 'x': 1 }], [{ 'x': 2 }, { 'x': 1 }], 'x');
29   * // => [{ 'x': 1 }, { 'x': 2 }]
30   */
31  var unionBy = baseRest(function(arrays) {
32    var iteratee = last(arrays);
33    if (isArrayLikeObject(iteratee)) {
34      iteratee = undefined;
35    }
36    return baseUniq(baseFlatten(arrays, 1, isArrayLikeObject, true), baseIteratee(iteratee, 2));
37  });
38  
39  module.exports = unionBy;