TRUE FALSE T; F logical(length = 0) as.logical(x) is.logical(x)
TRUE and FALSE are part of the R language, where
T and F are global variables set to these.
All four are logical(1) vectors.
logical creates a logical vector of the specified length.
Each element of the vector is equal to FALSE.
as.logical attempts to coerce its argument to be of logical
type.
is.logical returns TRUE or FALSE depending on
whether its argument is of logical type or not.