Create, coerce to or test for a double-precision vector.
double(length = 0) as.double(x, ...) is.double(x) single(length = 0) as.single(x, ...)
- 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.
- object to be coerced or tested.
- further arguments passed to or from other methods.
is.double is a test of double type.
R has no single precision data type. All real numbers are stored in double precision format. The functions
single are identical to
double except they set the attribute
Csingle that is used in the
.Fortran interface, and they are intended only to be used in that context.
double creates a double-precision vector of the specified length. The elements of the vector are all equal to
as.double attempts to coerce its argument to be of double type: like
as.vector it strips attributes including names. (To ensure that an object is of double type without stripping attributes, use
storage.mode.) Character strings containing optional whitespace followed by either a decimal representation or a hexadecimal representation (starting with
0X) can be converted, as can special values such as
"infinity", irrespective of case.
FALSE depending on whether its argument is of double type or not.
All R platforms are required to work with values conforming to the IEC 60559 (also known as IEEE 754) standard. This basically works with a precision of 53 bits, and represents to that precision a range of absolute values from about 2e-308 to 2e+308. It also has special values
NaN (many of them), plus and minus infinity and plus and minus zero (although R acts as if these are the same). There are also denormal(ized) (or subnormal) numbers with absolute values above or below the range given above but represented to less precision.
.Machine for precise information on these limits. Note that ultimately how double precision numbers are handled is down to the CPU/FPU and compiler.
In IEEE 754-2008/IEC60559:2011 this is called ‘binary64’ format.
Note on names
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.
http://grouper.ieee.org/groups/754/ for links to information on the standards.
Documentation reproduced from R 3.0.2. License: GPL-2.