factor(x, levels=sort(unique(x)), labels,
ordered=FALSE, exclude=NA)
ordered(x, levels=sort(unique(x)), labels, exclude=NA)
is.factor(x)
is.ordered(x)
is.unordered(x)
as.factor(x, ordered=FALSE)
factor is used to encode a vector as a factor
(the names category and enumerated type are also used for factors).
If ordered is TRUE, the factor levels are assumed ordered.
By default the levels are unordered.
For compatibility purposes, there is also a function called
ordered which provides an alternative way of creating
ordered factors.
The encoding of the vector happens as follows: if x[i]==levels[j]
then the i-th element of the result is j.
If no match is found for x[i] in levels, then the
i-th element of the result is set to NA.
Any values listed in exclude result in NAs
appearinging in the returned factor.
If exclude is set to a zero length vector, then any
NA values in x are used for form a new level
for the factor.
This means that there will be no NA
values in the result.
labels is a vector of character strings used to label
the levels of the factor.
The default is to use the encoded factor levels.
is.factor returns TRUE or FALSE
depending on whether its argument is of type factor or not.
Correspondingly, is.ordered (is.unordered)
returns TRUE when its argument is ordered (unordered)
and FALSE otherwise.
as.factor coerces its argument to a factor.
It is an abbreviated form of factor.
gl, levels, nlevels.