Roman Numerals

Description

Simple manipulation of (a small set of) integer numbers as roman numerals.

Usage

as.roman(x)
.romans

r1 + r2
r1 <= r2
max(r1)
sum(r2)

Arguments

Details

as.roman creates objects of class "roman" which are internally represented as integers, and have suitable methods for printing, formatting, subsetting, coercion, etc, see methods(class = "roman").

Arithmetic ("Arith"), Comparison ("Compare") and ("Logic"), i.e., all "Ops" group operations work as for regular numbers via R's integer functionality.

Only numbers between 1 and 3999 have a unique representation as roman numbers, and hence others result in as.roman(NA).

.romans is the basic dictionary, a named character vector.

References

Wikipedia contributors (2024). Roman numerals. Wikipedia, The Free Encyclopedia. https://en.wikipedia.org/w/index.php?title=Roman_numerals&oldid=1188781837. Accessed February 22, 2024.

Examples

## First five roman 'numbers'.
(y <- as.roman(1 : 5))
## Middle one.
y[3]
## Current year as a roman number.
(y <- as.roman(format(Sys.Date(), "%Y")))
## Today, and  10, 20, 30, and 100 years ago ...
y - 10*c(0:3,10)

## mixture of arabic and roman numbers :
as.roman(c(NA, 1:3, "", strrep("I", 1:6))) # + NA with a warning for "IIIIII"
cc <- c(NA, 1:3, strrep("I", 0:5))
(rc <- as.roman(cc)) # two NAs: 0 is not "roman"
(ic <- as.integer(rc)) # works automatically [without an explicit method]
rNA <- as.roman(NA)
## simple consistency checks -- arithmetic when result is in  {1,2,..,3999} :
stopifnot(identical(rc, as.roman(rc)), # as.roman(.) is "idempotent"
          identical(rc + rc + (3*rc), rc*5),
          identical(ic, c(NA, 1:3, NA, 1:5)),
          identical(as.integer(5*rc), 5L*ic),
          identical(as.numeric(rc), as.numeric(ic)),
          identical(rc[1], rNA),
          identical(as.roman(0), rNA),
          identical(as.roman(NA_character_), rNA),
          identical(as.list(rc), as.list(ic)))
## Non-Arithmetic 'Ops' :
stopifnot(exprs = {
        # Comparisons :
        identical(ic < 1:5, rc < 1:5)
        identical(ic < 1:5, rc < as.roman(1:5))
        # Logic  [integers |-> logical] :
        identical(rc & TRUE , ic & TRUE)
        identical(rc & FALSE, ic & FALSE)
        identical(rc | FALSE, ic | FALSE)
        identical(rc | NA   , ic | NA)
})
## 'Summary' group functions (and comparison):
(rc. <- rc[!is.na(rc)])
stopifnot(exprs = {
        identical(min(rc), as.roman(NA))
        identical(min(rc, na.rm=TRUE),
         as.roman(min(ic, na.rm=TRUE)))
        identical(range(rc.),
         as.roman(range(as.integer(rc.))))
        identical(sum (rc, na.rm=TRUE), as.roman("XXI"))
        identical(format(prod(rc, na.rm=TRUE)), "DCCXX")
        format(prod(rc.)) == "DCCXX"
})