lib/pivot-table.js
function createAggregator(setter, initializer) {
  return function(collection, iteratee) {
    var func = isArray_1(collection) ? _arrayAggregator : _baseAggregator,
        accumulator = initializer ? initializer() : {};

    return func(collection, setter, _baseIteratee(iteratee, 2), accumulator);
  };
}
function createAggregator(setter, initializer) {
  return function(collection, iteratee) {
    var func = isArray_1(collection) ? _arrayAggregator : _baseAggregator,
        accumulator = initializer ? initializer() : {};

    return func(collection, setter, _baseIteratee(iteratee, 2), accumulator);
  };
}
function createAggregator ( setter , initializer ) { return function ( collection , iteratee ) { var func = isArray_1 ( collection ) ? _arrayAggregator : _baseAggregator , accumulator = initializer ? initializer ( ) : { } ; return func ( collection , setter , _baseIteratee ( iteratee , 2 ) , accumulator ) ; } ; }
Creates a function like `_.groupBy`.

@private
@param {Function} setter The function to set accumulator values.
@param {Function} [initializer] The accumulator object initializer.
@returns {Function} Returns the new aggregator function.
Creates a function like _ . groupBy .