A non-destructive implementation of Table#select_columns that creates a new table (note this is not tested)

alt_select_columns.rb

  
    class Table

      def max_y
        @rows[0].length
      end

      def select_columns
        selected = (0..(max_y - 1)).map do |i|
          col = @rows.map {|row| row[i] }
          col if yield(col)
        end.compact.transpose

        if @header_support
          self.class.new [@headers] << selected, :headers => true
        else
          self.class.new selected, :headers => false
        end
      end

    end