Split string by space except what's inside parentheses

Question

I have the following string:

x <- "(((K05708+K05709+K05710+K00529) K05711),K05712) K05713 K05714 K02554"
# [1] "(((K05708+K05709+K05710+K00529) K05711),K05712) K05713 K05714 K02554"

and I want to split it by space delimiter avoiding what's inside the parentheses in order to have something like:

[[1]]
[1] "(((K05708+K05709+K05710 K00529) K05711),K05712)"                
[2] "K05713"                          "K05714"                         
[4] "K02554"

See that two spaces remain inside the first parentheses level.

I read the following answers but I couldn't make it work in my case: r split on delimiter not in parentheses and Using strsplit() in R, ignoring anything in parentheses

Thanks in advance!

Answer 1

I think you need a regex matching the balanced parentheses and then skipping them, and then matching the whitespaces that remain with the following PCRE-based regex:

(\((?:[^()]++|(?1))*\))(*SKIP)(*F)|\s

See the regex demo (replace the space with \s above for better visibility).

Pattern details:

• (\((?:[^()]++|(?1))*\))(*SKIP)(*F) - Group 1 matching
  • \((?:[^()]++|(?1))*\) - a substring presenting a balanced parentheses substring: \( matches a (, (?:[^()]++|(?1))* matches zero or more (*) sequences of 1+ chars other than ( and ) (see [^()]++) or the whole pattern of this whole Group 1 (see the subrouting call (?1)), then \) matches a literal ) and (*SKIP)(*F) make the regex discard the whole matched text while keeping the regex index at the end of that match, and proceed looking for the next match
• | - or
• - a space to split against

Here is an online R demo:

s <- "(((K05708+K05709+K05710+K00529) K05711),K05712) K05713 K05714 K02554"
strsplit(s, "(\\((?:[^()]++|(?1))*\\))(*SKIP)(*F)| ", perl=TRUE)

Output:

[[1]]
[1] "(((K05708+K05709+K05710+K00529) K05711),K05712)"
[2] "K05713"                                         
[3] "K05714"                                         
[4] "K02554"