| numeric {base} | R Documentation |
Creates or coerces objects of type "numeric".
is.numeric is a more general test of an object being
interpretable as numbers.
numeric(length = 0)
as.numeric(x, ...)
is.numeric(x)
length |
desired length. |
x |
object to be coerced or tested. |
... |
further arguments passed to or from other methods. |
numeric is identical to double (and real).
It creates a double-precision vector of the specified length with each
element equal to 0.
as.numeric is a generic function, but S3 methods must be
written for as.double. It is identical to
as.double (and as.real).
is.numeric is generic: you can write methods to handle
specific classes of objects, see InternalMethods. It is
not the same as is.double. Factors are handled
by the default method, and there are methods for classes
"Date" and "POSIXt" (in all three cases
the result is false). Methods for is.numeric should only
return true if the base type of the class is double or
integer and values can reasonably be regarded as
numeric (e.g. arithmetic on them makes sense).
for numeric and as.numeric see double.
The default method for is.numeric returns TRUE
if its argument is of mode "numeric"
(type "double" or type "integer") and not a
factor, and FALSE otherwise. That is,
is.integer(x) || is.double(x), or
(mode(x) == "numeric") && !is.factor(x).
as.numeric and is.numeric are internally S4 generic and
so methods can be set for them via setMethod.
To ensure that as.numeric, as.double and as.real
remain identical, S4 methods can only be set for as.numeric.
It is a historical anomaly that R has three names for its
floating-point vectors, double, numeric
and real.
double is the name of the type.
numeric is the name of the mode and also of the implicit
class. As an S4 formal class, use "numeric" (there was
a formal class "double" prior to R 2.7.0).
real is deprecated and should not be used in new code.
The potential confusion is that R has used mode
"numeric" to mean ‘double or integer’, which conflicts
with the S4 usage. Thus is.numeric tests the mode, not the
class, but as.numeric (which is identical to as.double)
coerces to the class.
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.
double, integer, storage.mode.
as.numeric(c("-.1"," 2.7 ","B")) # (-0.1, 2.7, NA) + warning
as.numeric(factor(5:10))