Regex to detect if all alphabetic characters are upper case

Question

How would I go about detecting if all alphabetic characters in a string (of >= 2 characters) are upper case? Ultimately, I'm trying to filter out chapter title names, that are rows in my data-set. So if a chapter title is "ARYA", I want that detected, same as "THE QUEEN'S HAND".

Here's what I'm trying but doesn't work:

library(dplyr)
library(stringr)

str_detect("THE QUEEN’S HAND", "^[[:upper:]]{2,}+$")
#> FALSE

The requirements I need:

• Number of characters >= 2 because I'm ultimately using this to filter out chapter names, but sometimes there's a row where the word is "I", but that's not a chapter -- it's just a word. Though this could be filtered at a different point
• Only alphabetic characters or apostrophes detected. Sometimes the row is "...", which I don't want detected. However, if I use a toupper(x) == (x) solution, this would be detected alongside something like "THE QUEEN'S HAND". I'm also trying to get rid of anything with exclamation points or periods, like "STOP THIS!"

Answer 1

Reverse your logic

all alphabetic characters are upper case.

is the same as

not a single alphabetic character is lower case.

Code

If you really want to use a regex for this task, all you need to write is :

! str_detect("THE QUEEN’S HAND", "[[:lower:]]")

You can test it here.

If you want to take the string length into account, you can add a logical OR :

nchar(str) < 2 || ! str_detect(str, "[[:lower:]]")

You can test it here.