Convert roman numerals to numbers in R

Tomas picture Tomas · Jan 14, 2014 · Viewed 8.6k times · Source

In R, there is a great function as.roman in the very base setup:

as.roman(79)
# [1] LXXIX

Is there an inverse function that would convert roman numerals to numbers?

(I know I can write it myself but I prefer to use already prepared or preferably standard functions, unfortunatelly cannot find one. Standard library or package function is a prefered solution)

Answer

gung - Reinstate Monica picture gung - Reinstate Monica · Jan 14, 2014

as.roman() returns an object of class roman, so R recognizes it as such. You can directly turn it back into an Arabic numeral with as.numeric(). If you have a string that meets the criteria such that it could be a valid roman numeral, you can coerce it to a class roman object with as.roman(), and then coerce it into an Arabic numeral by composing the coercion functions. Consider:

> as.roman(79)
[1] LXXIX
> x <- as.roman(79)
> x
[1] LXXIX
> str(x)
Class 'roman'  int 79
> as.roman("LXXIX")
[1] LXXIX
> as.numeric(as.roman("LXXIX"))
[1] 79