mode
for Categorical variables, one of either "factor" (default,
which returns the values as factor); "numeric" (which returns the numeric
values); or "id" (which returns the category ids). If "id", values
corresponding to missing categories will return as the underlying integer
codes; i.e., the R representation will not have any NA
s. Otherwise,
missing categories will all be returned NA
. For non-Categorical
variables, the mode
argument is ignored.