def set_cell(row_index, column_index, value)
      if within_range?(row_index, column_index)
        verify_against_column_type( @cols[column_index][:type], value )
        @rows[row_index][column_index] = GoogleVisualr::DataTable::Cell.new(value, @cols[column_index][:type])
      else
        raise RangeError, "row_index and column_index MUST be < @rows.size and @cols.size", caller
      end
    end
Sets the value (and formatted value) of a cell.

Parameters:
* row_index       [Required] A number greater than or equal to zero, but smaller than the total number of rows.
* column_index    [Required] A number greater than or equal to zero, but smaller than the total number of columns.
* value           [Required] The cell value.
The data type should match the column data type.
You can specify a value for a cell (e.g. 'hi').
Or specify a formatted value using cell objects (e.g. {v:55, f:'Fifty-five'}).