Made timeseries operation efficient for Pandas and DaskInterface

holoviews/operation/timeseries.py

@@ -5,6 +5,29 @@
 from ..core.util import pd
 from ..element import Scatter
 
+DF_INTERFACES = []
+try:
+    from ..core.data import PandasInterface
+    DF_INTERFACES.append(PandasInterface)
+except:
+    pass
+
+try:
+    from ..core.data import DaskInterface
+except:
+    DF_INTERFACES.append(DaskInterface)
+
+
+def get_df_data(element):
+    """
+    Return element data as dataframe, avoiding casting if already
+    in dataframe format
+    """
+    if element.interface in DF_INTERFACES:
+        return element.data
+    else:
+        return element.dframe()
+
 
 class rolling(ElementOperation):
     """
@@ -23,6 +46,7 @@ class rolling(ElementOperation):
 
     def _apply(self, element, key=None):
         xdim = element.kdims[0].name
+        df = get_df_data(element)
         df = df.rolling(window=self.p.rolling_window, center=self.p.center, on=xdim)
         return element.clone(df.apply(self.p.function).reset_index())
 
@@ -46,7 +70,7 @@ class resample(ElementOperation):
 
     def _apply(self, element, key=None):
         xdim = element.kdims[0].name
-        df = element.dframe()
+        df = get_df_data(element)
         df = df.resample(rule=self.p.rule, label=self.p.edge, on=xdim)
         return element.clone(df.apply(self.p.function).reset_index())