duplicates
character string specifying how to handle duplicated
country or country-time observations (for the latter see timeVar).
Can be set to none to do nothing, message to simply report
duplicates, drop to report and drop duplicates, and return to
return a data frame with only duplicated observations (see also
fromLast).
timeVar
character string indicating the name of a time variable. For
example, country time series often have separate rows based on a year
variable. This is used solely to determine if there are duplicated
country-time values.