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. One of these is used for the numeric missing value NA, and is.nan is false for that value. It is generic: you can write methods to handle specific classes of objects, see InternalMethods. The default method handles real and complex vectors: a complex number is regarded as NaN if either the real or imaginary part is NaN but not NA.

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)