#
# Show all possible input values:
#
a()
#
# Convert them in one letter-code:
#
aaa(a())
#
# Check consistency of results:
#
stopifnot(a(aaa(a())) == a())
#
# Show what happens with non-allowed values:
#
aaa("Z") # should be NA and a warning is generated
Run the code above in your browser using DataLab