R: 'Not Available' / Missing Values

NA {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 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)

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

    is.na(x) <- value

### Arguments

`x` | an R object to be tested: the default method for `is.na` handles atomic vectors, lists and pairlists: that for `anyNA` also handles `NULL`.
`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, see InternalMethods.

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 in `NA`: a possible exception is where `NaN` is also involved, in which case either might result. Logical computations treat `NA` as a missing `TRUE/FALSE` value, 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 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`, and `FALSE` otherwise. (A complex value is regarded as `NA` if either its real or imaginary part is `NA` or `NaN`.) `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.na` method for the class of the element is ignored).
For these types `anyNA` calls `is.na`.

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)` with a warning.

### 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
    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)))))
    }

    ## ... lists, and hence data frames, too:
    dN <- dd <- USJudgeRatings; dN[3,6] <- NA
    anyNA(dd) # FALSE
    anyNA(dN) # TRUE

[Package base version 3.1.2 Index]