factor(x, levels = sort(unique(x), na.last = TRUE), labels,
exclude = NA, ordered = FALSE)
ordered(x, levels = sort(unique(x), na.last = TRUE), labels,
exclude = NA, ordered = TRUE)
is.factor(x)
is.ordered(x)
as.factor(x, ordered = FALSE)
as.ordered(x)
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] equals
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 appearing in the
factor returned. 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.
factor applied to a factor is a no-op, except if there are
empty levels. In that case, a factor with the reduced level set
set is returned.
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 returns TRUE when its
argument is ordered and FALSE otherwise.
as.factor coerces its argument to a factor.
It is an abbreviated form of factor.
as.ordered(x) returns x if this is ordered, and
ordered(x) otherwise.
gl for construction of ``balanced'' factors;
levels and nlevels for accessing the
levels, and codes to get integer codes.
ff <- factor(substring("statistics",1:10,1:10), levels=letters)
ff
codes(ff)
factor(ff)
factor(factor(letters[7:10])[2:3]) # excercise indexing and reduction