How to extract string match within brackets in R?

Question

I want to extract "a", "b" from ["a", "b"], where the Content within [...] is not known before doing the Operation. So [...] is the only identifier.

Normally, the extraction works like

stringr::str_match(string = ["a", "b"]', pattern = "LEFT(.*?)RIGHT")

So i have to find sthg along:

stringr::str_match(string = '["a", "b"]', pattern = "[(.*?)]")

but have to escape the brackets i guess.

stringr::str_match(string = '["a", "b"]', pattern = "[[](.*?)[]]")

Probably, now the brackets are escaped, but not (.*?)?

What i tried:

• Normally, i would escape the bracket [ like [[] and use perl = TRUE. Therefore, i tried:

  stringr::str_match(string = '["a", "b"]', pattern = "[[](.*?)[]]") as shown above.

• Use regex like /[^[\]]+\[[^[\]]+\]/ from Extract string between brackets

Answer 1

We can use str_replace which would directly extract the elements

library(stringr)    
str_replace(str2, "\\[([^]]+)\\].*", "\\1")
#[1] "\"a\", \"b\""

Or with str_match

str_match(str2, "\\[([^]]+)")[,2]
#[1] "\"a\", \"b\""

data

str2 <- '["a", "b"]'

Answer 2

You can also use str_extractand positive lookbehind and lookahead:

str_extract(str1, "(?<=\\[).*(?=\\])")