code: public SortedGrouping<T> sortGroup(int field, Order order) {
  		return new SortedGrouping<T>(this.dataSet, this.keys, field, order);
  	}
docs: Sorts {@link Tuple} elements within a group on the specified field in the specified {@link Order}.</br>
  <b>Note: Only groups of Tuple elements can be sorted.</b><br/>
  Groups can be sorted by multiple fields by chaining {@link #sortGroup(int, Order)} calls.
  
  @param field The Tuple field on which the group is sorted.
  @param order The Order in which the specified Tuple field is sorted.
  @return A SortedGrouping with specified order of group element.
  
  @see Tuple
  @see Order