a list consisting of two objects:
predFrame a list of presorted and formatted predictor
information:
blockFac a matrix of zero-based factor predictor values.
blockFacSparse a sparse block of factor predictor values.
blockNum a matrix of dense numeric predictor values.
blockNumSparse a sparse block of numeric predictor values.
nPredFac the number of factor predictors.
nRow the number of training rows.
nPredFac the number of factor-valued predictors.
facCard a vector of the factor cardinalities.
nPredNum the number of numerical predictors.
signature a list consisting of training information needed
for separate testing and prediction:
predMap a vector mapping core indices to front-end counterparts.
colNames a vector of strings containing the training column
names.
rowNames a vector of strings containing the training row
names.
level a vector of strings containing the training response
factor levels.