def columns_indeces_to_drop columns
      result = []
      headers = @table[0]
      headers.each_with_index do |header, i|
        result << i unless columns.include? header
      end
      result
    end
def columns_indeces_to_drop columns
      result = []
      headers = @table[0]
      headers.each_with_index do |header, i|
        result << i unless columns.include? header
      end
      result
    end
Returns the column indeces to drop to make this table have the given columns