NA {base} | R Documentation |
NA
is a logical constant of length 1 which contains a missing
value indicator. NA
can be coerced to any other vector
type except raw. There are also constants NA_integer_
,
NA_real_
, NA_complex_
and NA_character_
of the
other atomic vector types which support missing values: all of these
are reserved words in the R language.
The generic function is.na
indicates which elements are missing.
The generic function is.na<-
sets elements to NA
.
NA is.na(x) ## S3 method for class 'data.frame' is.na(x) is.na(x) <- value
x |
an R object to be tested: the default method handles atomic vectors, lists and pairlists. |
value |
a suitable index vector for use with |
The NA
of character type is distinct from the
string "NA"
. Programmers who need to specify an explicit
string NA
should use NA_character_
rather than
"NA"
, or set elements to NA
using is.na<-
.
is.na(x)
works elementwise when x
is a
list
. It is generic: you can write methods to handle
specific classes of objects, see InternalMethods. A complex
value is regarded as NA
if either its real or imaginary part is
NA
or NaN
.
Function is.na<-
may provide a safer way to set missingness.
It behaves differently for factors, for example.
Computations using NA
will normally result in NA
: a
possible exception is where NaN
is also involved, in
which case either might result.
The default method for is.na
applied to an atomic vector
returns a logical vector of the same length as its argument x
,
containing TRUE
for those elements marked NA
or, for
numeric or complex vectors, NaN
(!) and FALSE
otherwise. dim
, dimnames
and names
attributes
are preserved.
The default methods also works for lists and pairlists:
For is.na
, elementwise the result is false unless that element
is a length-one atomic vector and the single element of that vector is
regarded as NA
or NaN
(note that any is.na
methods for the class of the atomic vector is ignored).
The data frame method for is.na
returns a logical matrix
with the same dimensions as the data frame, and with dimnames taken
from the row and column names of the data frame.
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.
Chambers, J. M. (1998) Programming with Data. A Guide to the S Language. Springer.
NaN
, is.nan
, etc.,
and the utility function complete.cases
.
na.action
, na.omit
, na.fail
on how methods can be tuned to deal with missing values.
is.na(c(1, NA)) #> FALSE TRUE is.na(paste(c(1, NA))) #> FALSE FALSE (xx <- c(0:4)) is.na(xx) <- c(2, 4) xx #> 0 NA 2 NA 4