Compacts the vector's index to include only those values that are present in the vector.
Extreme.Numerics (in Extreme.Numerics.dll) Version: 8.1.1
member Compact : unit -> unit
A categorical vector contains a mapping of values and corresponding level indexes.
If this mapping is not fixed, it is possible that it contains values
that are no longer present in the vector. Calling this method ensures that the
growth of the mapping is kept in check.