function arrayAggregator(array, setter, iteratee, accumulator) {
    var index = -1,
        length = array.length;

    while (++index < length) {
      var value = array[index];
      setter(accumulator, value, iteratee(value), array);
    }
    return accumulator;
  }
A specialized version of `baseAggregator` for arrays.

@private
@param {Array} array The array to iterate over.
@param {Function} setter The function to set `accumulator` values.
@param {Function} iteratee The iteratee to transform keys.
@param {Object} accumulator The initial aggregated object.
@returns {Function} Returns `accumulator`.