All possible combinations from regex pattern in R

Question

How to get all possible combinations from the following regex pattern?

"(ost|west)europäisch(*$|e(*$|r|s|n|m))"

I would like getting a vector that looks like this:

[1] "osteuropäisch"    "westeuropäisch"   "osteuropäische"   "westeuropäische" 
[5] "osteuropäischer"  "westeuropäischer" "osteuropäisches"  "westeuropäisches"
[9] "osteuropäischen"  "westeuropäischen" "osteuropäischem"  "westeuropäischem"

From the following question, I understand that I can get all combinations with the following function:

do.call(paste0, expand.grid(
   c("ost","west"),
   "europäisch",
   c("", paste0("e", c("", "r", "s", "n", "m"))))
)

However, I have a large number of different regex patterns that I need to convert into full strings. Therefore, I was wondering if there is anywhere a function or package for R that can transform regex expressions into a vector of all possible combinations.

So far I have not found any explicit function in base, stringi or stringr

From a similar question on regex combinations in python, I know that for python the exrex module exists. I was thinking that maybe something similar exists for R, which I am not able to find?

Answer 1

This almost works for your example - you could easily encapsulate it in a function. I don't know if it will break for different/more exotic examples ...

(This doesn't quite work right for the "*$" before "e": e.g. is "westeuropäischm", with no "e" between "h" and "m" shouldn't be an option?

str <- "(ost|west)europäisch(*$|e(*$|r|s|n|m))"
s1 <- strsplit(str, "[()]")[[1]]
s1 <- s1[nzchar(s1)]
s2 <- strsplit(s1, "\\|")
s2 <- lapply(s2, gsub, pattern = "\\*|\\$", replacement = "")
s3 <- do.call(expand.grid, s2)
res <- apply(s3, 1, paste, collapse = "")

Check:

grepl(str, res)

(doesn't quite work yet)