1  var baseIteratee = require('./_baseIteratee'),
 2      baseSum = require('./_baseSum');
 3  
 4  /**
 5   * This method is like `_.sum` except that it accepts `iteratee` which is
 6   * invoked for each element in `array` to generate the value to be summed.
 7   * The iteratee is invoked with one argument: (value).
 8   *
 9   * @static
10   * @memberOf _
11   * @since 4.0.0
12   * @category Math
13   * @param {Array} array The array to iterate over.
14   * @param {Function} [iteratee=_.identity] The iteratee invoked per element.
15   * @returns {number} Returns the sum.
16   * @example
17   *
18   * var objects = [{ 'n': 4 }, { 'n': 2 }, { 'n': 8 }, { 'n': 6 }];
19   *
20   * _.sumBy(objects, function(o) { return o.n; });
21   * // => 20
22   *
23   * // The `_.property` iteratee shorthand.
24   * _.sumBy(objects, 'n');
25   * // => 20
26   */
27  function sumBy(array, iteratee) {
28    return (array && array.length)
29      ? baseSum(array, baseIteratee(iteratee, 2))
30      : 0;
31  }
32  
33  module.exports = sumBy;