An add-on to the 'party' package, with a faster implementation
of the partial-conditional permutation importance for random forests. The
standard permutation importance is implemented exactly the same as in
the 'party' package. The conditional permutation importance can be
computed faster, with an option to be backward compatible to the 'party'
implementation. The package is compatible with random forests fit using the
'party' and the 'randomForest' package. The methods are described in
Strobl et al. (2007)