R/roman2int.R

In gtools: Various R Programming Tools

testConvert <- function() {
  roman <- "IVXLCDM"
  retval <- romandigit.convert(roman)
  stopifnot(retval == c(1, 5, 10, 50, 100, 500, 1000))
  return(TRUE)
}

romandigit.convert <- function(roman) {
  retval <- .C(C_convert,
    roman = as.character(roman),
    nchar = as.integer(nchar(roman)),
    values = integer(nchar(roman)),
    PACKAGE = "gtools"
  )
  retval$values
}

roman2int.inner <- function(roman) {
  results <- .C(C_roman2int,
    roman = as.character(roman),
    nchar = as.integer(nchar(roman)),
    value = integer(1),
    PACKAGE = "gtools"
  )

  return(results$value)
}



#' Convert Roman Numerals to Integers
#'
#' Convert roman numerals to integers
#'
#' This function will convert roman numerals to integers without the upper bound
#' imposed by R (3899), ignoring case.
#'
#' @param roman character vector containing roman numerals
#' @return A integer vector with the same length as \code{roman}.  Character
#' strings which are not valid roman numerals will be converted to \code{NA}.
#' @author Gregory R. Warnes \email{greg@@warnes.net}
#' @seealso \code{\link[utils]{as.roman}}
#' @keywords arith
#' @examples
#'
#' roman2int(c("I", "V", "X", "C", "L", "D", "M"))
#'
#' # works regardless of case
#' roman2int("MMXVI")
#' roman2int("mmxvi")
#'
#' # works beyond R's limit of 3899
#' val.3899 <- "MMMDCCCXCIX"
#' val.3900 <- "MMMCM"
#' val.4000 <- "MMMM"
#' as.numeric(as.roman(val.3899))
#' as.numeric(as.roman(val.3900))
#' as.numeric(as.roman(val.4000))
#'
#' roman2int(val.3899)
#' roman2int(val.3900)
#' roman2int(val.4000)
#' @export
roman2int <- function(roman) {
  roman <- trimws(toupper(as.character(roman)))

  tryIt <- function(x) {
    retval <- try(roman2int.inner(x), silent = TRUE)
    if (is.numeric(retval)) {
      retval
    } else {
      NA
    }
  }

  retval <- sapply(roman, tryIt)

  retval
}