You can group Best Match search results by category. To group by category, put the BestMatchCategoryGroup value in the OrderBy field. When you use the BestMatchCategoryGroup value, you can include group parameters in your call. Note that there will be significanty fewer results returned with a BestMatchCategoryGroup sort because the results account for Best Matches in lower-level (leaf) as well as higher-level categories. There is not a direct correlation between the number of results returned in a regular sort or the number of results returned with a BestMatch sort, and the results that are returned by the BestMatchCategoryGroup sort. You should not receive more than 2 pages of results with this type of sort. See also the new GroupCategoryID element in ItemType.
See the
Field Index to learn which calls use Group.