I have a table with a row for each bike facility occurrence in each VA county and the trails in each county. I want to summarize that data. It can be done using Categories in Numbers. Under Organize, select Add Categories. This will sort the table and create a new row for each category. Cells in that row can be designated to Sum the values in that column. The Category was Locality and the Length of each facility segment is totaled by clicking the gears in the category row for that attribute. All Categories can be collapsed and the total for Length calculated by selecting the category totals and pasting them into another sheet and totaling those.