## Not Available / ``Missing'' Values

## Usage

    NA
    is.na(x)

## 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.

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

## 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

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