Use labels in tagger

spacy/pipeline/tagger.pyx

@@ -266,7 +266,7 @@ class Tagger(Pipe):
             raise ValueError("nan value when computing loss")
         return float(loss), d_scores
 
-    def initialize(self, get_examples, *, nlp=None):
+    def initialize(self, get_examples, *, nlp=None, labels=None):
         """Initialize the pipe for training, using a representative set
         of data examples.
 
@@ -277,15 +277,19 @@ class Tagger(Pipe):
         DOCS: https://nightly.spacy.io/api/tagger#initialize
         """
         self._ensure_examples(get_examples)
+        if labels is not None:
+            for tag in labels:
+                self.add_label(tag)
+        else:
+            tags = set()
+            for example in get_examples():
+                for token in example.y:
+                    if token.tag_:
+                        tags.add(token.tag_)
+            for tag in sorted(tags):
+                self.add_label(tag)
         doc_sample = []
         label_sample = []
-        tags = set()
-        for example in get_examples():
-            for token in example.y:
-                if token.tag_:
-                    tags.add(token.tag_)
-        for tag in sorted(tags):
-            self.add_label(tag)
         for example in islice(get_examples(), 10):
             doc_sample.append(example.x)
             gold_tags = example.get_aligned("TAG", as_string=True)