R: 'Not Available' / Missing Values (original) (raw)
Description
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.
The generic function anyNA implements any(is.na(x)) in a possibly faster way (especially for atomic vectors).
Usage
NA
is.na(x)
anyNA(x, recursive = FALSE)
## S3 method for class 'data.frame'
is.na(x)
is.na(x) <- value
Arguments
| x | an R object to be tested: the default method foris.na and anyNA handle atomic vectors, lists, pairlists, and NULL. |
|---|---|
| recursive | logical: should anyNA be applied recursively to lists and pairlists? |
| value | a suitable index vector for use with x. |
Details
The NA of character type is distinct from the string"NA". Programmers who need to specify an explicit missing string should use NA_character_ (rather than "NA") or set elements to NA using is.na<-.
is.na and anyNA are generic: you can write methods to handle specific classes of objects, seeInternalMethods.
Function is.na<- may provide a safer way to set missingness. It behaves differently for factors, for example.
Numerical computations using NA will normally result inNA: a possible exception is where [NaN](../../base/help/NaN.html) is also involved, in which case either might result (which may depend on the R platform). However, this is not guaranteed and future CPUs and/or compilers may behave differently. Dynamic binary translation may also impact this behavior (with valgrind, computations using NAmay result in NaN even when no NaN is involved).
Logical computations treat NA as a missing TRUE/FALSEvalue, and so may return TRUE or FALSE if the expression does not depend on the NA operand.
The default method for anyNA handles atomic vectors without a class and NULL. It calls any(is.na(x)) on objects with classes and for recursive = FALSE, on lists and pairlists.
Value
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](../../base/help/NaN.html), and FALSEotherwise. (A complex value is regarded as NA if either its real or imaginary part is NA or [NaN](../../base/help/NaN.html).)dim, dimnames and names attributes are copied to the result.
The default methods also work 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.namethod for the class of the element is ignored).anyNA(recursive = FALSE) works the same way as is.na;anyNA(recursive = TRUE) applies anyNA (with method dispatch) to each element.
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.
anyNA(NULL) is false; is.na(NULL) is logical(0)(no longer warning since R version 3.5.0).
References
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.
See Also
[NaN](../../base/help/NaN.html), [is.nan](../../base/help/is.nan.html), etc., and the utility function [complete.cases](../../stats/html/complete.cases.html).
[na.action](../../stats/html/na.action.html), [na.omit](../../stats/html/na.fail.html), [na.fail](../../stats/html/na.fail.html)on how methods can be tuned to deal with missing values.
Examples
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
anyNA(xx) # TRUE
# Some logical operations do not return NA
c(TRUE, FALSE) & NA
c(TRUE, FALSE) | NA
## Measure speed difference in a favourable case:
## the difference depends on the platform, on most ca 3x.
x <- 1:10000; x[5000] <- NaN # coerces x to be double
if(require("microbenchmark")) { # does not work reliably on all platforms
print(microbenchmark(any(is.na(x)), anyNA(x)))
} else {
nSim <- 2^13
print(rbind(is.na = system.time(replicate(nSim, any(is.na(x)))),
anyNA = system.time(replicate(nSim, anyNA(x)))))
}
## anyNA() can work recursively with list()s:
LL <- list(1:5, c(NA, 5:8), c("A","NA"), c("a", NA_character_))
L2 <- LL[c(1,3)]
sapply(LL, anyNA); c(anyNA(LL), anyNA(LL, TRUE))
sapply(L2, anyNA); c(anyNA(L2), anyNA(L2, TRUE))
## ... lists, and hence data frames, too:
dN <- dd <- USJudgeRatings; dN[3,6] <- NA
anyNA(dd) # FALSE
anyNA(dN) # TRUE
[Package _base_ version 4.6.0 Index]