# roman: Roman Numerals

Description Usage Arguments Details References Examples

## Description

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

## Usage

 ```1 2 3 4 5 6 7``` ```as.roman(x) .romans r1 + r2 r1 <= r2 max(r1) sum(r2) ```

## Arguments

 `x` a numeric or character vector of arabic or roman numerals. `r1, r2` a roman number vector, i.e., of `class` `"roman"`.

## 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 3899 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 (2006). Roman numerals. Wikipedia, The Free Encyclopedia. https://en.wikipedia.org/w/index.php?title=Roman_numerals&oldid=78252134. Accessed September 29, 2006.

## Examples

 ``` 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48``` ```## First five roman 'numbers'. (y <- as.roman(1 : 5)) ## Middle one. y ## 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,..,3899} : 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, 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" }) ```