`is.finite`

and `is.infinite`

return a vector of the same
length as `x`

, indicating which elements are finite (not infinite
and not missing) or infinite.

`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.) `Inf`

and `NaN`

are
reserved words in the R language.

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

x

R object to be tested: the default methods handle atomic vectors.

A logical vector of the same length as `x`

: `dim`

,
`dimnames`

and `names`

attributes are preserved.

`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`

) and `FALSE`

otherwise. 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`

) and `FALSE`

otherwise. This will be false unless `x`

is numeric or complex.
Complex numbers are infinite if either the real or the 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. A complex number is regarded as `NaN`

if
either the real or imaginary part is `NaN`

but not `NA`

.
All elements of logical, integer and raw vectors are considered not to
be NaN.

All three functions accept `NULL`

as input and return a length
zero result. The default methods accept character and raw vectors, and
return `FALSE`

for all entries. Prior to R version 2.14.0 they
accepted all input, returning `FALSE`

for most non-numeric
values; cases which are not atomic vectors are now signalled as
errors.

All three functions are generic: you can write methods to handle specific classes of objects, see InternalMethods.

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

https://en.wikipedia.org/wiki/NaN.

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

The C99 function `isfinite`

is used for `is.finite`

.

`NA`

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

```
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)
```

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