numeric Numeric Vectors

Description

Creates or coerces objects of type "numeric". is.numeric is a more general test of an object being interpretable as numbers.

Usage

numeric(length = 0)
as.numeric(x, ...)
is.numeric(x)

Arguments

length	A non-negative integer specifying the desired length. Double values will be coerced to integer: supplying an argument of length other than one is an error.
x	object to be coerced or tested.
...	further arguments passed to or from other methods.

Details

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.

is.numeric is an internal generic primitive function: 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", "POSIXt" and "difftime" (all of which return 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, and comparison should be done via the base type).

Value

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).

Warning

If x is a factor, as.numeric will return the underlying numeric (integer) representation, which is often meaningless as it may not correspond to the factor levels, see the ‘Warning’ section in factor (and the 2nd example below).

S4 methods

as.numeric and is.numeric are internally S4 generic and so methods can be set for them via setMethod.

To ensure that as.numeric and as.double remain identical, S4 methods can only be set for as.numeric.

Note on names

It is a historical anomaly that R has two names for its floating-point vectors, double and numeric (and formerly had 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".

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.

References

Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.

See Also

double, integer, storage.mode.

Examples

## Conversion does trim whitespace; non-numeric strings give NA + warning
as.numeric(c("-.1"," 2.7 ","B"))

## Numeric values are sometimes accidentally converted to factors.
## Converting them back to numeric is trickier than you'd expect.
f <- factor(5:10)
as.numeric(f) # not what you might expect, probably not what you want
## what you typically meant and want:
as.numeric(as.character(f))
## the same, considerably more efficient (for long vectors):
as.numeric(levels(f))[f]