|  | var baseFlatten = require('./_baseFlatten'), | 
|  | baseIteratee = require('./_baseIteratee'), | 
|  | baseRest = require('./_baseRest'), | 
|  | baseUniq = require('./_baseUniq'), | 
|  | isArrayLikeObject = require('./isArrayLikeObject'), | 
|  | last = require('./last'); | 
|  |  | 
|  | /** | 
|  | * This method is like `_.union` except that it accepts `iteratee` which is | 
|  | * invoked for each element of each `arrays` to generate the criterion by | 
|  | * which uniqueness is computed. Result values are chosen from the first | 
|  | * array in which the value occurs. The iteratee is invoked with one argument: | 
|  | * (value). | 
|  | * | 
|  | * @static | 
|  | * @memberOf _ | 
|  | * @since 4.0.0 | 
|  | * @category Array | 
|  | * @param {...Array} [arrays] The arrays to inspect. | 
|  | * @param {Function} [iteratee=_.identity] The iteratee invoked per element. | 
|  | * @returns {Array} Returns the new array of combined values. | 
|  | * @example | 
|  | * | 
|  | * _.unionBy([2.1], [1.2, 2.3], Math.floor); | 
|  | * // => [2.1, 1.2] | 
|  | * | 
|  | * // The `_.property` iteratee shorthand. | 
|  | * _.unionBy([{ 'x': 1 }], [{ 'x': 2 }, { 'x': 1 }], 'x'); | 
|  | * // => [{ 'x': 1 }, { 'x': 2 }] | 
|  | */ | 
|  | var unionBy = baseRest(function(arrays) { | 
|  | var iteratee = last(arrays); | 
|  | if (isArrayLikeObject(iteratee)) { | 
|  | iteratee = undefined; | 
|  | } | 
|  | return baseUniq(baseFlatten(arrays, 1, isArrayLikeObject, true), baseIteratee(iteratee, 2)); | 
|  | }); | 
|  |  | 
|  | module.exports = unionBy; |