logical
Logical Objects
Description
Creates or tests for objects of mode logical.
Usage
logical(length = 0L)
is.logical(x)
as.logical(x, ...)
## S3 method for class 'factor':
as.logical(x, ...)
Arguments
| length |
the desired length for the resulting object.
|
| x |
any object.
|
| ... |
additional arguments for particular methods.
|
Details
as.logical is generic and primitive. Only one method for a factor object is implemented at present.
There is no default method for generic as.logical.
Logical objects are coerced automatically to numeric for arithmetic
and other numeric computations. In the coercion, TRUE becomes 1 and
FALSE becomes 0.
Conversely, numeric objects are coerced to logical by setting all
non-zero values to TRUE. Note that this practice allows for no rounding
error, so it is not a good practice, except in the case where computations are known
to have integer results.
When a vector of mode "character" is passed to it,
as.logical coerces the character strings "F", "FALSE", "False", and "false"
to FALSE; it coerces the character strings "T", "TRUE", "True", and "true" to TRUE;
it coerces all other strings to NA.
When a factor is passed to it, as.logical.factor uses levels(x)[x] as input and calls as.logical as usual.
Note the difference between coercing to a simple object of mode
"logical"
and setting the
mode attribute:
mode(myobject) <- "logical"
The above example changes the mode of myobject,
but it leaves all other attributes unchanged
(so, for example, a matrix stays a matrix); whereas
the value of as.logical(myobject) has no attributes.
Value
| logical | returns a simple object of mode "logical",
of the specified length. |
| is.logical | returns TRUE if x has mode
"logical". Otherwise, it returns FALSE.
Its behavior is unaffected by attributes of x; for example,
x could be a logical array (in contrast to the behavior of
is.vector). |
| as.logical | returns x if x is a simple object
of mode "logical". Otherwise, it returns a logical object of the
same length as x, with data resulting from coercing the elements
of x to mode "logical". |
See Also
Examples
zz <- c(-pi, 0.0, pi, NA) # sample object
logical(length(zz)) # logical object same length as zz
as.logical(zz)
as.logical(c("T", "F", "T", "T"))
f <- factor(c("T", "false", "test", "F", "NULL", "TRUE"))
as.logical(f)