stringr equivalent to grep

Sorry for the late answer but it might be helpful for future visitors:

Now you can use str_which(string, pattern) which is a wrapper around which(str_detect(string, pattern)) and equivalent to grep(pattern, string).

str_which(LETTERS, "F|Y")
[1]  6 25

More details at: http://stringr.tidyverse.org/reference/str_subset.html