# # The logical class

Logical is a mode (and an implicit class) for vectors.

## # Logical operators

There are two sorts of logical operators: those that accept and return vectors of any length (elementwise operators: `!`

, `|`

, `&`

, `xor()`

) and those that only evaluate the first element in each argument (`&&`

, `||`

). The second sort is primarily used as the `cond`

argument to the `if`

function.

Logical Operator | Meaning | Syntax |
---|---|---|

! | Not | !x |

& | element-wise (vectorized) and | x & y |

&& | and (single element only) | x && y |

element-wise (vectorized) or | ||

xor | element-wise (vectorized) exclusive OR | xor(x,y) |

Note that the `||`

operator evaluates the left condition and if the left condition is TRUE the right side is never evaluated. This can save time if the first is the result of a complex operation. The `&&`

operator will likewise return FALSE without evaluation of the second argument when the first element of the first argument is FALSE.

```
> x <- 5
> x > 6 || stop("X is too small")
Error: X is too small
> x > 3 || stop("X is too small")
[1] TRUE
```

To check whether a value is a logical you can use the `is.logical()`

function.

## # Coercion

To coerce a variable to a logical use the `as.logical()`

function.

```
> x <- 2
> z <- x > 4
> z
[1] FALSE
> class(x)
[1] "numeric"
> as.logical(2)
[1] TRUE
```

When applying `as.numeric()`

to a logical, a double will be returned. `NA`

is a logical value and a logical operator with an `NA`

will return `NA`

if the outcome is ambiguous.

## # Interpretation of NAs

See Missing values for details.

```
> TRUE & NA
[1] NA
> FALSE & NA
[1] FALSE
> TRUE || NA
[1] TRUE
> FALSE || NA
[1] NA
```

#### # Remarks

### # Shorthand

`TRUE`

, `FALSE`

and `NA`

are the only values for logical vectors; and all three are reserved words. `T`

and `F`

can be shorthand for `TRUE`

and `FALSE`

in a clean R session, but neither `T`

nor `F`

are reserved, so assignment of non-default values to those names can set users up for difficulties.