droplevels is used to drop unused levels from a
factor or, more commonly, from factors in a data frame.
# S3 method for factor droplevels(x, exclude = if(anyNA(levels(x))) NULL else NA, …) # S3 method for data.frame droplevels(x, except, exclude, …)
an object from which to drop unused factor levels.
factor(); factor levels which
should be excluded from the result even if present. Note that this
NA in R <= 3.3.1 which did drop
NA levels even when present in
x, contrary to the
documentation. The current default is compatible with
x[ , drop=TRUE].
further arguments passed to methods
indices of columns from which not to drop levels
droplevels returns an object of the same class as
The method for class
"factor" is currently equivalent to
factor(x, exclude=exclude). For the data frame method, you
should rarely specify
exclude “globally” for all factor
columns; rather the default uses the same factor-specific
exclude as the factor method itself.
except argument follow the usual indexing rules.