numeric(n=0) as.numeric(x) is.numeric(x)
numeric creates a real vector of length n.
The vector is filled with zeros.
as.numeric attempts to coerce
its argument to numeric type (either integer or real).
is.numeric returns true if its argument is of
type real or type integer and false otherwise.
Note
R has no single precision data type.
All real numbers are stored in double precision format.