How do I split apart a CSV string in Ruby?

Question

I have this line as an example from a CSV file:

2412,21,\"Which of the following is not found in all cells?\",\"Curriculum\",\"Life and Living Processes, Lif         


        

Answer 1

This is not a suitable task for regular expressions. You need a CSV parser, and Ruby has one built in:

http://ruby-doc.org/stdlib/libdoc/csv/rdoc/classes/CSV.html

And an arguably superior 3rd part library:

http://fastercsv.rubyforge.org/

Answer 2

EDIT: I failed to read the Ruby tag. The good news is, the guide will explain the theory behind building this, even if the language specifics aren't right. Sorry.

Here is a fantastic guide to doing this:

http://knab.ws/blog/index.php?/archives/10-CSV-file-parser-and-writer-in-C-Part-2.html

and the csv writer is here:

http://knab.ws/blog/index.php?/archives/3-CSV-file-parser-and-writer-in-C-Part-1.html

These examples cover the case of having a quoted literal in a csv (which may or may not contain a comma).

Answer 3

My preference is @steenstag's solution, but an alternative is to use String#scan with the following regular expression.

r = /(?<![^,])(?:(?!")[^,\n]*(?<!")|"[^"\n]*")(?![^,])/

If the variable str holds the string given in the example, we obtain:

puts str.scan r

displays

2412
21
"Which of the following is not found in all cells?"
"Curriculum"
"Life and Living Processes, Life Processes"


1
0
"endofline"

Start your engine!

See also regex101 which provides a detailed explanation of each token of the regex. (Move your cursor across the regex.)

Ruby's regex engine performs the following operations.

(?<![^,]) : negative lookbehind assert current location is not preceded
            by a character other than a comma
(?:       : begin non-capture group
  (?!")   : negative lookahead asserts next char is not a double-quote
  [^,\n]* : match 0+ chars other than a comma and newline
  (?<!")  : negative lookbehind asserts preceding character is not a
            double-quote
  |       : or
  "       : match double-quote
  [^"\n]* : match 0+ chars other than double-quote and newline
  "       : match double-quote
)         : end of non-capture group
(?![^,])  : negative lookahead asserts current location is not followed
            by a character other than a comma

Note that (?<![^,]) is the same as (?<=,|^) and (?![^,]) is the same as (?=^|,).

Answer 4

This morning I stumbled across a CSV Table Importer project for Ruby-on-Rails. Eventually you will find the code helpful:

Github TableImporter

Answer 5

str=<<EOF
2412,21,"Which of the following is not found in all cells?","Curriculum","Life and Living Processes, Life Processes",,,1,0,"endofline"
EOF
require 'csv' # built in

p CSV.parse(str)
# That's it! However, empty fields appear as nil.
# Makes sense to me, but if you insist on empty strings then do something like:
parser = CSV.new(str)
parser.convert{|field| field.nil? ? "" : field}
p parser.readlines

Answer 6

text=<<EOF
2412,21,"Which of the following is not found in all cells?","Curriculum","Life and Living Processes, Life Processes",,,1,0,"endofline"
EOF
x=[]
text.chomp.split("\042").each_with_index do |y,i|
  i%2==0 ?  x<< y.split(",") : x<<y
end
print x.flatten

output

$ ruby test.rb
["2412", "21", "Which of the following is not found in all cells?", "Curriculum", "Life and Living Processes, Life Processes", "", "", "", "1", "0", "endofline"]