base (version 3.0.3)

double: Double-Precision Vectors

Description

Create, coerce to or test for a double-precision vector.

Usage

double(length = 0)
as.double(x, ...)
is.double(x)
single(length = 0)
as.single(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.

Value

double creates a double-precision vector of the specified length. The elements of the vector are all equal to 0.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 or 0X) can be converted, as can special values such as "NA", "NaN", "Inf" and "infinity", irrespective of case.as.double for factors yields the codes underlying the factor levels, not the numeric representation of the labels, see also factor.is.double returns TRUE or FALSE depending on whether its argument is of double type or not.

Double-precision values

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. See .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

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.

Details

double creates a double-precision vector of the specified length. The elements of the vector are all equal to 0. It is identical to numeric.

as.double is a generic function. It is identical to as.numeric. Methods should return an object of base type "double".

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 as.single and single are identical to as.double and double except they set the attribute Csingle that is used in the .C and .Fortran interface, and they are intended only to be used in that context.

References

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

http://en.wikipedia.org/wiki/IEEE_754-1985, http://en.wikipedia.org/wiki/IEEE_754-2008, http://en.wikipedia.org/wiki/Double_precision, http://en.wikipedia.org/wiki/Denormal_number.

http://grouper.ieee.org/groups/754/ for links to information on the standards.

See Also

integer, numeric, storage.mode.

Examples

is.double(1)
all(double(3) == 0)