I was recently participating in a coding challenge which involved converting integers to Roman numerals. I knew R offers this functionality already via as.roman() and hoped to leverage that for a quick solution, but was surprised that one of the challenge's tests failed; conversion of the number 3999, which should result in "MMMCMXCIX". In R, that produces NA.
I looked into the source and documentation and it's clear that an upper limit of 3899 is enforced in several places, and documented as such. I detailed some of these explorations on my blog [0]. Ben Bolker traced the first implementation (or at the least the creation of src/library/utils/R/roman.R) in the (GitHub cloned) source [1] dating back to 2006 and this uses the 3899 hard limit. Wikipedia [2] claims the largest uniquely representable Roman numeral is 3999. Other languages appear to use 3999 as the largest input value, e.g. the python-cookbook [3]. Common lisp's "~@r" format errors with values larger than 3999 ``` (print (format nil "~@r" 4000)) *** - The ~@R format directive requires an integer in the range 1 - 3999, not 4000 ``` Is 3899 enforced as the largest valid input in R for some other reason, or is this a long-standing oversight? Perhaps tangentially... while exploring I did notice the unexported utils:::.as.roman() takes a check.range argument that is not available from as.roman (which is simply an exported wrapper without that argument) but setting this to FALSE does not enable circumvention of enforcement of the upper limit (which appears to occur during the setting of the "roman" class), it simply performs an earlier conversion to NA when set (potentially for simplification when used in Ops dispatch). Enforcement of the limit of 3899 happens deeper within the code, e.g. within the unexported utils:::.numeric2roman which implements the conversion, but without a way to avoid setting the result to NA for larger values. Given that other languages strictly limit the input to an upper bound, perhaps this is not unexpected behaviour. Regards, - Jonathan. [0]: https://jcarroll.xyz/2024/02/10/friends-romans-countrymen.html [1]: https://github.com/r-devel/r-svn/commit/ba30f3dc716effe22489bf88511bd1d60272f6de [2]: https://en.wikipedia.org/wiki/Roman_numerals [3]: https://www.oreilly.com/library/view/python-cookbook/0596001673/ch03s24.html ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
