Special Values
There are a few special values that are used in R.
NA
In R, the NA
values are
used to represent missing values. (NA
stands for “not available.”) You
may encounter NA
values in text
loaded into R (to represent missing values) or in data loaded from
databases (to replace NULL
values).
If you expand the size of a vector (or matrix or array) beyond the
size where values were defined, the new spaces will have the value
NA
:
> v <- c(1,2,3) > v [1] 1 2 3 > length(v) <- 4 > v [1] 1 2 3 NA
Inf and -Inf
If a computation results in a number that is too big, R
will return Inf
for a positive number
and -Inf
for a negative number
(meaning positive and negative infinity, respectively):
> 2 ^ 1024 [1] Inf > - 2 ^ 1024 [1] -Inf
This is also the value returned when you divide by 0:
> 1 / 0 [1] Inf
NaN
Sometimes, a computation will produce a result that makes
little sense. In these cases, R will often return NaN
(meaning “not a number”):
> Inf - Inf [1] NaN > 0 / 0 [1] NaN
NULL
Additionally, there is a null object in R, represented by
the symbol NULL
. (The symbol NULL
always points to the same object.)
NULL
is often used as an argument in
functions to mean that no value was assigned to the argument.
Additionally, some functions may return NULL
. Note that NULL
is not the same as NA
, Inf
,
-Inf
, or NaN
.
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