Finite, Infinite and NaN Numbers

Description

is.finite and is.infinite return a vector of the same length as x, indicating which elements are finite (not infinite and not missing).

Inf and -Inf are positive and negative “infinity” whereas NaN means “Not a Number”. (These apply to numeric values and real and imaginary parts of complex values but not to values of integer vectors.)

Usage

is.finite(x)
is.infinite(x)
Inf
NaN
is.nan(x)

Arguments

Details

is.finite returns a vector of the same length as x the jth element of which is TRUE if x[j] is finite (i.e., it is not one of the values NA, NaN, Inf or -Inf). All elements of types other than logical, integer, numeric and complex vectors are false. Complex numbers are finite if both the real and imaginary parts are.

is.infinite returns a vector of the same length as x the jth element of which is TRUE if x[j] is infinite (i.e., equal to one of Inf or -Inf). This will be false unless x is numeric or complex. Complex numbers are infinite if either the real and imaginary part is.

is.nan tests if a numeric value is NaN. Do not test equality to NaN, or even use identical, since systems typically have many different NaN values. In most ports of R one of these is used for the numeric missing value NA. It is generic: you can write methods to handle specific classes of objects, see InternalMethods.

Note

In R, basically all mathematical functions (including basic Arithmetic), are supposed to work properly with +/- Inf and NaN as input or output.

The basic rule should be that calls and relations with Infs really are statements with a proper mathematical limit.

References

The IEC 60559 standard, also know as the ANSI/IEEE 754 Floating-Point Standard.

D. Goldberg (1991) What Every Computer Scientist Should Know about Floating-Point Arithmetic ACM Computing Surveys, 23(1).
Postscript version available at http://www.validlab.com/goldberg/paper.ps Extended PDF version at http://www.validlab.com/goldberg/paper.pdf

http://grouper.ieee.org/groups/754/ for accessible information.

The C99 function isfinite is used for is.finite if available.

See Also

NA, ‘Not Available’ which is not a number as well, however usually used for missing values and applies to many modes, not just numeric.

Examples

pi / 0 ## = Inf a non-zero number divided by zero creates infinity
0 / 0  ## =  NaN

1/0 + 1/0# Inf
1/0 - 1/0# NaN

stopifnot(
    1/0 == Inf,
    1/Inf == 0
)
sin(Inf)
cos(Inf)
tan(Inf)