Can I specify mandatory arguments with optparse

Question

I am using the optparse package but cannot find out if I can specify mandatory arguments.

install.packages('optparse')
library('optparse')
library('data.table')

# example from vignette
option_list <- list(
  # those 2 are linked together by dest='verbose'
  # store_true makes sure it does not take any arg by storing TRUE (or default if specified)
  make_option(c("-v", "--verbose"), action="store_true", default=TRUE, help="Print extra output [default %default]"),
  make_option(c("-q", "--quietly"), action="store_false", dest="verbose", help="Print little output"),
  #
  make_option(c("-c", "--count"), type="integer", default=5L, help="Number of rgn [default %default]", metavar="number"),
  make_option("--generator", default="rnorm", help = "Function to generate random deviates [default \"%default\"]")
)
parser <- OptionParser(option_list=option_list)

# vanilla case
parsedArgs <- parse_args(parser, args = c("-c","100","--generator","fakeGen"))
setcolorder(setDT(stack(parsedArgs)),c('ind','values'))[]
#         ind  values
#1:   verbose    TRUE
#2:     count     100
#3: generator fakeGen
#4:      help   FALSE

Say I want the user to input a [-d --date SOMEDATE] it does not really make sense to provide a default date... how can I tell optparse that some args are mandatory ?

Answer 1

According to its documentation, it does not seem that mandatory functionality is implemented by optparse package.

However, as a workaround, you can always check for the parameter value and stop() the script execution in case the parameter is not set.

One approach could be like:

install.packages('optparse')
library('optparse')
library('data.table')

# example from vignette
option_list <- list(
  make_option(c("-v", "--verbose"), action="store_true", default=TRUE, help="Print extra output [default %default]"),
  make_option(c("-q", "--quietly"), action="store_false", dest="verbose", help="Print little output"),
  make_option(c("-c", "--count"), type="integer", default=5L, help="Number of rgn [default %default]", metavar="number"),
  make_option("--generator", default="rnorm", help = "Function to generate random deviates [default \"%default\"]"),
  make_option(c("-d", "--date"), action = "store", default = NA, type = 'character',
              help = "some date to be converted from character")
)
parser <- OptionParser(option_list=option_list)

# check date is provided
if (!is.na(parser$date)) {
  mydate <- as.Date(parser$date)
}
else {
  stop("date parameter must be provided. See script usage (--help)")
}

By setting date's default value as NA we can check later if it was supplied.

Note: since date will contain user's input you should do some checks and/or handle the likely error issued by as.Date() function if it is not able to parse the given parameter option.