Tutorial by Topics: missing

ParameterDetailsmethodThe name of the method that has been called (in the above example this is :say_moo, note that this is a symbol.*argsThe arguments passed in to this method. Can be any number, or none&blockThe block of the method called, this can either be a do block, or a { } enclosed bloc...

Should we include the non-documented ffill and bfill?

When we don't know the value a variable takes, we say its value is missing, indicated by NA. Missing values are represented by the symbol NA (not available). Impossible values (e.g., as a result of sqrt(-1)) are represented by the symbol NaN (not a number).