support grouped collections

fiftyone/core/collections.py

@@ -7728,17 +7728,19 @@ def count(self, field_or_expr=None, expr=None, safe=False):
         """
 
         # Optimization: use estimated document count when possible
-        if (
-            isinstance(self, fod.Dataset)
-            and expr is None
+        if self._is_full_collection() and (
+            expr is None
             and (
                 field_or_expr is None
-                or (field_or_expr == "frames" and self._has_frame_fields())
+                or (
+                    etau.is_str(field_or_expr)
+                    and field_or_expr == "frames"
+                    and self._has_frame_fields()
+                )
             )
         ):
             frames = field_or_expr == "frames"
-            # pylint: disable=no-member
-            return self._estimated_count(frames=frames)
+            return self._dataset._estimated_count(frames=frames)
 
         make = lambda field_or_expr: foa.Count(
             field_or_expr, expr=expr, safe=safe
@@ -10616,6 +10618,22 @@ def _has_frame_fields(self):
     def _handle_id_fields(self, field_name):
         return _handle_id_fields(self, field_name)
 
+    def _is_full_collection(self):
+        if isinstance(self, fod.Dataset) and self.media_type != fom.GROUP:
+            return True
+
+        # pylint:disable=no-member
+        if (
+            isinstance(self, fov.DatasetView)
+            and self._dataset.media_type == fom.GROUP
+            and len(self._stages) == 1
+            and isinstance(self._stages[0], fos.SelectGroupSlices)
+            and self._pipeline() == []
+        ):
+            return True
+
+        return False
+
     def _is_label_field(self, field_name, label_type_or_types):
         try:
             label_type = self._get_label_field_type(field_name)