Fast, lightweight toolkit for data splitting. Data
sets can be partitioned into disjoint groups (e.g. into training,
validation, and test) or into (repeated) k-folds for subsequent
cross-validation. Besides basic splits, the package supports
stratified, grouped as well as blocked splitting. Furthermore,
cross-validation folds for time series data can be created. See e.g.
Hastie et al. (2001)