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rroman-numerals

Convert roman numerals to numbers in R

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'd prefer to use already prepared or preferably standard library functions.

Solution

  • 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