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
(meaning “not
available”):
> 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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