StaticCarveCarve the locked holdout off matrix.
the assembled rows (rows with no label already removed)
the pipeline's LockedHoldoutFraction
the label column; when it is not in the matrix the carve is a plain seeded sample
classification carves are stratified on the label; regression carves are not
the split seed (normally DEFAULT_SPLIT_SEED)
StaticHoldoutHow many rows a fraction holds out of total: at least one when the fraction is positive, never every row (one
row always stays for training), and none when there is at most one row.
Seeded, stratified locked-holdout carve. Pure; no I/O.