code: def create_file_header(columns)
          columns.each_with_index do |c,i|
            next if i == @current_key
            columns[i] = c.scan(Regexp.new(@current_source_header)).flatten[0]
          end
  
          @file_header = @current_key ? [@current_key.to_i] : []
  
          header_cols.each do |h|
            @file_header << columns.index(h) 
          end 
  
          @file_header.compact!
        end
docs: create a filter for the columns that match the header filter