Up to Filtered Summary version 2.5, there was no built-in way to aggregate by multiple columns. The best way to aggregate by multiple columns is to concatenate the columns together in an adjacent column.
With the introduction of Essentials Bundle 3, multiple column aggregation support was added. Simply concatenate the columns you would like to aggregate with a comma separator (ex: “3,2” would aggregate using the third and second column in your source data).
More details are covered here:
http://centigonsolutions.com/documentation/essentials/index.html#infowindow