Not Available / “Missing” Values

Description

NA is a logical constant of length 1 which contains a missing value indicator. NA can be freely 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.

Usage

NA
is.na(x)
## S3 method for class 'data.frame'
is.na(x)

is.na(x) <- value

Arguments

Details

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.

Value

The default method for is.na returns a logical vector of the same length as its argument x, containing TRUE for those elements marked NA or NaN (!) and FALSE otherwise. dim, dimnames and names attributes are preserved.

The method is.na.data.frame 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.

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, 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.

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