code: public TableSliceGroup splitOn(String... columns) {
          return splitOn(categoricalColumns(columns).toArray(new CategoricalColumn<?>[columns.length]));
      }
docs: Returns a non-overlapping and exhaustive collection of "slices" over this table.
  Each slice is like a virtual table containing a subset of the records in this table
  
  This method is intended for advanced or unusual operations on the subtables.
  If you want to calculate summary statistics for each subtable, the summarize methods (e.g)
  
  table.summarize(myColumn, mean, median).by(columns)
  
  are preferred