         Groups = []     # [] Array over categories :: {category: Category, metrics[]: Array of Metric}
         Cols = []       # [] Array over metrics :: {category: Category, metric: Metric} (flattened version of Groups)
         Rows = []       # [i] :: Row (-1 => foot)
+        Cats = {}       # Set of used categories
         Order = []      # Permutation Array of Row in display order
         Expanded = undefined # Info
 

            when 'release'
              cn = constants.release[v]
              cell.className = cn + ' release icon hint-release-' + cn
              #if slot.top
              #  cell.classList.add('null')
              v = ''
            when 'date'
              #if slot.top
              #  cell.classList.add('null')
            when 'age'
              v = display.formatAge(v)
            else

            return

          add: (c, d) ->
            Cats[c] = true
            if v = this[c]
              if Array.isArray(v)
                n = v.push(d) - 1
