logical {base}

R Documentation

Logical Vectors

Description

Create or test for objects of type "logical", and the basic logical constants.

Usage

TRUE
FALSE
T; F

logical(length = 0)
as.logical(x, ...)
is.logical(x)

Arguments

length	a non-negative integer specifying the desired length. Double values will be coerced to integer: supplying an argument of length other than one is an error.
x	object to be coerced or tested.
...	further arguments passed to or from other methods.

Details

TRUE and FALSE are reserved words denoting logical constants in the R language, whereas T and F are global variables whose initial values set to these. All four are logical(1) vectors.

as.logical is a generic function. Methods should return an object of type "logical".

Logical vectors are coerced to integer vectors in contexts where a numerical value is required, with TRUE being mapped to 1L, FALSE to 0L and NA to NA_integer_.

Value

logical creates a logical vector of the specified length. Each element of the vector is equal to FALSE.

as.logical attempts to coerce its argument to be of logical type. In numeric and complex vectors, zeros are FALSE and non-zero values are TRUE. For factors, this uses the levels (labels). Like as.vector it strips attributes including names. Character strings c("T", "TRUE", "True", "true") are regarded as true, c("F", "FALSE", "False", "false") as false, and all others as NA.

is.logical returns TRUE or FALSE depending on whether its argument is of logical type or not.

References

Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.

See Also

NA, the other logical constant. Logical operators are documented in Logic.

Examples

## non-zero values are TRUE
as.logical(c(pi,0))
if (length(letters)) cat("26 is TRUE\n")

## logical interpretation of particular strings
charvec <- c("FALSE", "F", "False", "false",    "fAlse", "0",
             "TRUE",  "T", "True",  "true",     "tRue",  "1")
as.logical(charvec)

## factors are converted via their levels, so string conversion is used
as.logical(factor(charvec))
as.logical(factor(c(0,1)))  # "0" and "1" give NA

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