code: public static StandardTableSliceGroup create(Table original, String... columnsNames) {
          List<CategoricalColumn<?>> columns = original.categoricalColumns(columnsNames);
          return new StandardTableSliceGroup(original, columns.toArray(new CategoricalColumn<?>[0]));
      }
docs: Returns a viewGroup splitting the original table on the given columns.
  The named columns must be CategoricalColumns