Question

POSIX Expression is giving me a headache.

Lets say we have a string:

a = "[question(37), question_pipe(\"Person10\")]"

and ultimately I would like to be able to have:

b = c("37", "Person10")

I’ve had a look at the stringr package but cant figure out how to extract the information out using regular expressions and str_split.

Any help would be greatly appreciated.

Cameron

Answer 1

So if I understand correctly you want to extract the elements within parenthesis.

You can first extract those elements, including the parenthesis, using str_extract_all:

b1 <- str_extract_all(string = a, pattern = "\\(.*?\\)")
b1
# [[1]]
# [1] "(37)"           "(\"Person10\")"

Since str_extract_all returns a list, let’s turn it into a vector:

b2 <- unlist(b1)
b2
# [1] "(37)"           "(\"Person10\")"

Last, you can remove the parenthesis (the first and last character of each string) using str_sub:

b3 <- str_sub(string = b2, start = 2L, end = -2L) 
b3
# [1] "37"           "\"Person10\""

Edit: A few comments about the regex pattern: \\( and \\) are your opening and closing parenthesis. .*? means any character string but without being greedy, otherwise you would get one long match from the first ( to the last ).