Creates an extractor for extracting slice keys.

The incoming Extracts must contain features stored under tfma.FEATURES_KEY and optionally under tfma.TRANSFORMED_FEATURES.

The extractor's PTransform yields a copy of the Extracts input with an additional extract pointing at the list of SliceKeyType values keyed by tfma.SLICE_KEY_TYPES_KEY. If materialize is True then a materialized version of the slice keys will be added under the key tfma.SLICE_KEYS_KEY.

slice_spec Deprecated (use EvalConfig).
eval_config Optional EvalConfig containing slicing_specs specifying the slices to slice the data into. If slicing_specs are empty, defaults to overall slice.
materialize True to add MaterializedColumn entries for the slice keys.

Extractor for slice keys.