Capitalizing text in R with an exception list

Question

*Apologies, I should've been more clear (I really appreciate all the help though!)

I extract from a database a .csv file. This file contains a list of place names. I use INITCAP when I extract them so they are all proper mixed case. However some of these place names need to remain capitalized as they are know abbreviations, like universities, etc. The end result will be me putting this back into the database in a corrected format.

I'm new to R and stuck on a bit of a problem. I'm extracting data that is all in capitals but I need it to be proper case i.e. change, "THIS IS ALL CAPS" to "This Is All Caps" but I need to be able to exclude certain words. Things like "FYI" and other abbreviations need to remain capitalized. I've managed to solve some of my issue with the lettercase library, particularly str_ucfirst. My only remaining issue is the exception part. Any suggestions would be appreciated. Thanks.

Answer 1

Building on @akrun's (now deleted) solution you could form an exception vector which is then paste0d into a regular expression using (*SKIP)(*FAIL):

string <- "THIS IS ALL CAPS"
exceptions <- c("FYI", "THIS")
pattern <- sprintf("(?:%s)(*SKIP)(*FAIL)|\\b([A-Z])(\\w+)", paste0(exceptions, collapse = "|"))
gsub(pattern, "\\1\\L\\2", string, perl = TRUE)

Which yields

[1] "THIS Is All Caps"

Note the THIS which got ignored.

---

The pattern is

unimportant|not_important|(very important)

In terms of regex engines that support it, this is

...(*SKIP)(*FAIL)|what_i_want_to_match

In this case

\b      # a word boundary
([A-Z]) # uppercase letters
(\w+)   # [a-zA-Z0-9_]+

This is fed into the replacement subroutine.