Regex to extract pattern from string until a symbol occurs, or the string ends

user_11825057 0
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I have an issue where I want to extract a pattern from a vector of strings, ie extract c("TAG a", "TAG b", "TAG c") from c("TAG a", "TAG b-3", "TAG c+3")

So far I've tried:

str_vec <- c("TAG a", "TAG b-3", "TAG c+2", "2+TAG d")

stringr::str_extract(str_vec, "TAG .*(?=[\\+\\-])")

Which returns TAG b and c correctly, but doesn't extract TAG a or d.

If I try

stringr::str_extract(str_vec, "TAG .*(?=[\\+\\-]|$)")

TAG a and d are returned correclty, but $ seems to override +/- so TAG b and c are returned with their suffixes still attached.

stringr r regex
2 Answers

How about:

library(stringr)

str_extract(str_vec, "TAG [a-z]")

Output:

[1] "TAG a" "TAG b" "TAG c" "TAG d"
user_47864660

You need

str_vec <- c("TAG a", "TAG b-3", "TAG c+2", "2+TAG d")
stringr::str_extract(str_vec, "TAG [^+-]*")
# => [1] "TAG a" "TAG b" "TAG c" "TAG d"

Details:

  • TAG - a fixed string
  • [^+-]* - zero or more chars other than - and +.

See the regex demo and the R demo.

user_38329700
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