NA                   package:base                   R Documentation

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.

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

     The generic function `is.na<-' sets elements to `NA'.

Usage:

     NA
     is.na(x)
     is.na.data.frame(x)

     is.na(x) <- value

Arguments:

       x: an R object to be tested.

   value: a suitable index vector for use with `x'.

Details:

     For character vectors the value `"NA"' represents missingness.

     `is.na(x)' works elementwise when `x' is a `list'. The method
     dispatching is C-internal, rather than via `UseMethod'.

     Function `is.na<-' may provide a safer way to set missingness. It
     behaves differently for factors, for example.

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))       #> F TRUE
     is.na(paste(c(1,NA)))#> F FALSE

