Split string in Ruby, ignoring contents of parentheses?

Question

I need to split a string into a list of parts in Ruby, but I need to ignore stuff inside paramentheses. For example:

A +4, B +6, C (hello, goodbye) +5, D +3

I'd like the resulting list to be:

[0]A +4
[1]B +6
[2]C (hello, goodbye) +5
[3]D +3

But I can't simply split on commas, because that would split the contents of the parentheses. Is there a way to split stuff out without pre-parsing the commas in the braces into something else?

Thanks.

Beware of frowny faces :-( messing up the parse! – Myrddin Emrys Jan 06 '10 at 20:19 — Myrddin Emrys, Jan 06 '10 at 20:19

score 13 · Accepted Answer · edited Jan 06 '10 at 20:51

13

Try this:

s = 'A +4, B +6, C (hello, goodbye) +5, D +3'
tokens = s.scan(/(?:\(.*?\)|[^,])+/)
tokens.each {|t| puts t.strip}

Output:

A +4
B +6
C (hello, goodbye) +5
D +3

A short explanation:

(?:        # open non-capturing group 1
  \(       #   match '('
  .*?      #   reluctatly match zero or more character other than line breaks
  \)       #   match ')'
  |        #   OR
  [^,]     #   match something other than a comma
)+         # close non-capturing group 1 and repeat it one or more times

Another option is to split on a comma followed by some spaces only when the first parenthesis that can be seen when looking ahead is an opening parenthesis (or no parenthesis at all: ie. the end of the string):

s = 'A +4, B +6, C (hello, goodbye) +5, D +3'
tokens = s.split(/,\s*(?=[^()]*(?:\(|$))/)
tokens.each {|t| puts t}

will produce the same output, but I find the scan method cleaner.

edited Jan 06 '10 at 20:51

Bob Aman

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answered Jan 06 '10 at 20:17

Bart Kiers

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# => ["A +4", " B +6", " C (hello, goodbye) +5", " D +3"] Looks perfect to me. Might want to #trim it to remove surrounding whitespace. – Myrddin Emrys Jan 06 '10 at 20:24
this does not work for `A +4, B +6, C (hello, (how are you?, bad)goodbye) +5, D +3`. Any idea how to fix it please? – rochb Jan 30 '11 at 18:35
@rochb, when an arbitrary number of nested parenthesis come into play, use a proper parser, don't go hacking with regex. – Bart Kiers Jan 30 '11 at 19:08

gabriel · Answer 2 · 2010-01-06T21:33:23.410

6

string = "A +4, B +6, C (hello, goodbye) +5, D +3"
string.split(/ *, *(?=[^\)]*?(?:\(|$))/)
# => ["A +4", "B +6", "C (hello, goodbye) +5", "D +3"]

How this regex works:

/
   *, *        # find comma, ignoring leading and trailing spaces.
  (?=          # (Pattern in here is matched against but is not returned as part of the match.)
    [^\)]*?    #   optionally, find a sequence of zero or more characters that are not ')'
    (?:        #   <non-capturing parentheses group>
      \(       #     left paren ')'
      |        #     - OR -
      $        #     (end of string)
    )
  )
/

edited Jan 06 '10 at 21:33

answered Jan 06 '10 at 20:30

gabriel

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That may be a bit cryptic without an explanation for the faint hearted regex-enthusiast the OP probably is! :). But a good solution nevertheless. – Bart Kiers Jan 06 '10 at 20:38
How does this work? I couldn't find any good documentation about how regex worked with split - like Bart K. says I'm not that great with regexes – Colen Jan 06 '10 at 20:53
@Colen, I posted a very similar regex as a second solution including an explanation. – Bart Kiers Jan 06 '10 at 20:54

Split string in Ruby, ignoring contents of parentheses?

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