Add get_slices_if_not_provided to data/dataset.py

combo/data/dataset.py

 import logging
 
+from combo import data
 
 logger = logging.getLogger(__name__)
 
@@ -7,5 +8,30 @@ logger = logging.getLogger(__name__)
 class DatasetReader:
     pass
 
+
 class UniversalDependenciesDatasetReader(DatasetReader):
-    pass
+    pass
\ No newline at end of file
+
+
+def get_slices_if_not_provided(vocab: data.Vocabulary):
+    if hasattr(vocab, "slices"):
+        return vocab.slices
+
+    if "feats_labels" in vocab.get_namespaces():
+        idx2token = vocab.get_index_to_token_vocabulary("feats_labels")
+        for _, v in dict(idx2token).items():
+            if v not in ["_", "__PAD__"]:
+                empty_value = v.split("=")[0] + "=None"
+                vocab.add_token_to_namespace(empty_value, "feats_labels")
+
+        slices = {}
+        for idx, name in vocab.get_index_to_token_vocabulary("feats_labels").items():
+            # There are 2 types features: with (Case=Acc) or without assigment (None).
+            # Here we group their indices by name (before assigment sign).
+            name = name.split("=")[0]
+            if name in slices:
+                slices[name].append(idx)
+            else:
+                slices[name] = [idx]
+        vocab.slices = slices
+        return vocab.slices