HORIZON PROJECT

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;