Question

I’m generating some CSV output using Ruby’s built-in CSV. Everything works fine, but the customer wants the name field in the output to have wrapping double-quotes so the output looks like the input file. For instance, the input looks something like this:

1,1.1.1.1,"Firstname Lastname",more,fields
2,2.2.2.2,"Firstname Lastname, Jr.",more,fields

CSV’s output, which is correct, looks like:

1,1.1.1.1,Firstname Lastname,more,fields
2,2.2.2.2,"Firstname Lastname, Jr.",more,fields

I know CSV is doing the right thing by not double-quoting the third field just because it has embedded blanks, and wrapping the field with double-quotes when it has the embedded comma. What I’d like to do, to help the customer feel warm and fuzzy, is tell CSV to always double-quote the third field.

I tried wrapping the field in double-quotes in my to_a method, which creates a "Firstname Lastname" field being passed to CSV, but CSV laughed at my puny-human attempt and output """Firstname Lastname""". That is the correct thing to do because it’s escaping the double-quotes, so that didn’t work.

Then I tried setting CSV’s :force_quotes => true in the open method, which output double-quotes wrapping all fields as expected, but the customer didn’t like that, which I expected also. So, that didn’t work either.

I’ve looked through the Table and Row docs and nothing appeared to give me access to the "generate a String field" method, or a way to set a "for field n always use quoting" flag.

I’m about to dive into the source to see if there’s some super-secret tweaks, or if there’s a way to monkey-patch CSV and bend it to do my will, but wondered if anyone had some special knowledge or had run into this before.

And, yes, I know I could roll my own CSV output, but I prefer to not reinvent well-tested wheels. And, I’m also aware of FasterCSV; That’s now part of Ruby 1.9.2, which I’m using, so explicitly using FasterCSV buys me nothing special. Also, I’m not using Rails and have no intention of rewriting it in Rails, so unless you have a cute way of implementing it using a small subset of Rails, don’t bother. I’ll downvote any recommendations to use any of those ways just because you didn’t bother to read this far.

Answer 1

Well, there’s a way to do it but it wasn’t as clean as I’d hoped the CSV code could allow.

I had to subclass CSV, then override the CSV::Row.<<= method and add another method forced_quote_fields= to make it possible to define the fields I want to force-quoting on, plus pull two lambdas from other methods. At least it works for what I want:

require 'csv'

class MyCSV < CSV
    def <<(row)
      # make sure headers have been assigned
      if header_row? and [Array, String].include? @use_headers.class
        parse_headers  # won't read data for Array or String
        self << @headers if @write_headers
      end

      # handle CSV::Row objects and Hashes
      row = case row
        when self.class::Row then row.fields
        when Hash            then @headers.map { |header| row[header] }
        else                      row
      end

      @headers = row if header_row?
      @lineno  += 1

      @do_quote ||= lambda do |field|
        field         = String(field)
        encoded_quote = @quote_char.encode(field.encoding)
        encoded_quote                                +
        field.gsub(encoded_quote, encoded_quote * 2) +
        encoded_quote
      end

      @quotable_chars      ||= encode_str("\r\n", @col_sep, @quote_char)
      @forced_quote_fields ||= []

      @my_quote_lambda ||= lambda do |field, index|
        if field.nil?  # represent +nil+ fields as empty unquoted fields
          ""
        else
          field = String(field)  # Stringify fields
          # represent empty fields as empty quoted fields
          if (
            field.empty?                          or
            field.count(@quotable_chars).nonzero? or
            @forced_quote_fields.include?(index)
          )
            @do_quote.call(field)
          else
            field  # unquoted field
          end
        end
      end

      output = row.map.with_index(&@my_quote_lambda).join(@col_sep) + @row_sep  # quote and separate
      if (
        @io.is_a?(StringIO)             and
        output.encoding != raw_encoding and
        (compatible_encoding = Encoding.compatible?(@io.string, output))
      )
        @io = StringIO.new(@io.string.force_encoding(compatible_encoding))
        @io.seek(0, IO::SEEK_END)
      end
      @io << output

      self  # for chaining
    end
    alias_method :add_row, :<<
    alias_method :puts,    :<<

    def forced_quote_fields=(indexes=[])
      @forced_quote_fields = indexes
    end
end

That’s the code. Calling it:

data = [ 
  %w[1 2 3], 
  [ 2, 'two too',  3 ], 
  [ 3, 'two, too', 3 ] 
]

quote_fields = [1]

puts "Ruby version:   #{ RUBY_VERSION }"
puts "Quoting fields: #{ quote_fields.join(', ') }", "\n"

csv = MyCSV.generate do |_csv|
  _csv.forced_quote_fields = quote_fields
  data.each do |d| 
    _csv << d
  end
end

puts csv

results in:

# >> Ruby version:   1.9.2
# >> Quoting fields: 1
# >> 
# >> 1,"2",3
# >> 2,"two too",3
# >> 3,"two, too",3