A method is disclosed for removing redundancies from a list of data structures. A list of data structures is sorted by first attribute into sub-lists having a common first attribute. Each of these sub-lists is sorted by second attribute into sub-lists having a common first attribute and a common second attribute. Each of these sub-lists is combined into a single combined data structure that includes a third attribute set. Each third attribute set includes third attributes of the data structures in the sub-list from which the combined data structure including that set was formed.