SolrQuery::setGroupMain() - If true, the result of the first field grouping command is used as the main result list in the response, using group.format=simple
SolrQuery::setGroupNGroups() - If true, Solr includes the number of groups that have matched the query in the results
SolrQuery::setGroupTruncate() - If true, facet counts are based on the most relevant document of each group matching the query