intersectionBy.js

var arrayMap = require('./_arrayMap'),
    baseIntersection = require('./_baseIntersection'),
    baseIteratee = require('./_baseIteratee'),
    baseRest = require('./_baseRest'),
    castArrayLikeObject = require('./_castArrayLikeObject'),
    last = require('./last');

/**
 * This method is like `_.intersection` except that it accepts `iteratee`
 * which is invoked for each element of each `arrays` to generate the criterion
 * by which they're compared. The order and references of result values are
 * determined by the first array. 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 intersecting values.
 * @example
 *
 * _.intersectionBy([2.1, 1.2], [2.3, 3.4], Math.floor);
 * // => [2.1]
 *
 * // The `_.property` iteratee shorthand.
 * _.intersectionBy([{ 'x': 1 }], [{ 'x': 2 }, { 'x': 1 }], 'x');
 * // => [{ 'x': 1 }]
 */
var intersectionBy = baseRest(function(arrays) {
  var iteratee = last(arrays),
      mapped = arrayMap(arrays, castArrayLikeObject);

  if (iteratee === last(mapped)) {
    iteratee = undefined;
  } else {
    mapped.pop();
  }
  return (mapped.length && mapped[0] === arrays[0])
    ? baseIntersection(mapped, baseIteratee(iteratee, 2))
    : [];
});

module.exports = intersectionBy;