I have a vector of data in R that has entries like data = BURR_WK_94_91and I want to extract the number that falls between the two underscores. So in this case get 94. The strings are of variable length so I can't use a starting position.
I'm almost there with this answer
library(qdap)
genXtract(data, "_", "_")
But that gives me extra data that I don't need. Is there a way to query if the string is a number between the underscores then extract it?
Yes, for example using lookbehind and lookahead with regex.
data = "BURR_WK_94_91"
gsub(".*(?<=_)(\\d+)(?=_).*", "\\1", data, perl = TRUE)
[1] "94"
Or, using stringr package, you only have to match the exact group.
stringr::str_extract_all(data, "(?<=_)((\\d+)*)(?=_)")
[[1]]
[1] "94"
One approach would be to use:
gsub(".*_(\\d+)_.*", "\\1", "BURR_WK_94_91", perl = T)
(\\d+) - denotes a capture group - capture any number of digits
\\1 - back reference to the first capture group
.*_ - any number of characters ending with a _
_.* - any number of characters starting with a _
So basically what you telling the function to do is to replace everything with the capture group.
if there is exactly 2 digits:
gsub(".*_(\\d{2})_.*", "\\1", "BURR_WK_94_91", perl = T)
You can use str_match from the stringr package
stringr::str_match(data, "_([0-9]{2})_") %>%
magrittr::extract(,2)
