Draft for the Dataframe interchange protocol

packages/vaex-core/vaex/dataframe.py

@@ -41,6 +41,7 @@
 from .datatype import DataType
 from .docstrings import docsubst
 
+
 astropy = vaex.utils.optional_import("astropy.units")
 
 # py2/p3 compatibility
@@ -246,6 +247,12 @@ def dep_filter(d : dict):
         fp = vaex.cache.fingerprint(state, df.dataset.fingerprint)
         return f'dataframe-{fp}'
 
+    def __dataframe__(self, nan_as_null : bool = False, allow_copy : bool = True):
+        """
+        """
+        import vaex.dataframe_protocol
+        return vaex.dataframe_protocol._VaexDataFrame(self, nan_as_null=nan_as_null, allow_copy=allow_copy)
+
     def _future(self, version=5, inplace=False):
         '''Act like a Vaex dataframe version 5.
 
@@ -5488,6 +5495,9 @@ def _auto_encode_data(self, expression, values):
             return values
         if self.is_category(expression):
             dictionary = vaex.array_types.to_arrow(self.category_labels(expression))
+            offset = self.category_offset(expression)
+            if offset != 0:
+                values = values - offset
             values = vaex.array_types.to_arrow(values)
             to_type = None
             if values.type in self._dict_mapping: