I'm trying to convert the Roman numerals in a string to Arabic. 

I tried using `stringr::str_sub` to select the corresponding characters and use `as.numeric(as.roman())` to convert, but it's messier than I thought.

```
A <- c("Case I", "Big Case II", "Not a Case", "This is Case IV")

```

I expect the output to be:

```
"Case 1" "Big Case 2" "Not a Case" "This is Case 4"

```