Enum-like arguments in R

Question

I\'m new to R and I\'m currently trying to supply the enumeration-like argument to the R function (or the RC/R6 class method), I currently use character vector plus ma

Answer 1

Update 07/21/2017: I have created a package for enumerations in R:

https://github.com/aryoda/R_enumerations

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If you want to use self-defined enum-alike data types as arguments of R functions that support

• automatic translation of enum item names to the corresponding integer values
• code auto completion (e. g. in RStudio)
• clear documentation in the function signature which values are allowed as actual function parameters
• easy validation of the actual function parameter against the allowed (integer) enum item values

you can define your own match.enum.arg function, e. g.:

match.enum.arg <- function(arg, choices) {
  if (missing(choices)) {
    formal.args <- formals(sys.function(sys.parent()))
    choices <- eval(formal.args[[as.character(substitute(arg))]])
  }

  if(identical(arg, choices))
    arg <- choices[[1]][1]    # choose the first value of the first list item

  allowed.values <- sapply(choices,function(item) {item[1]})   # extract the integer values of the enum items

  if(!is.element(arg, allowed.values))
    stop(paste("'arg' must be one of the values in the 'choices' list:", paste(allowed.values, collapse = ", ")))

  return(arg)
}

Usage:

You can then define and use your own enums like this:

ColorEnum <- list(BLUE = 1L, RED = 2L, BLACK = 3L)

color2code = function(enum = ColorEnum) { 
  i <- match.enum.arg(enum)
  return(i)
}

Example calls:

> color2code(ColorEnum$RED) # use a value from the enum (with auto completion support)
[1] 2
> color2code()              # takes the first color of the ColorEnum
[1] 1
> color2code(3)             # an integer enum value (dirty, just for demonstration)
[1] 3
> color2code(4)             # an invalid number
Error in match.enum.arg(enum) : 
  'arg' must be one of the values in the 'choices' list: 1, 2, 3