Add start/stop/plot to DataFrame

The latter passes on to hvplot (will fail if not importable)

Author: Martin Durant

streamz/collection.py

@@ -232,6 +232,12 @@ def _repr_html_(self):
     def current_value(self):
         return self.stream.current_value
 
+    def start(self):
+        self.stream.start()
+
+    def stop(self):
+        self.stream.stop()
+
     def _ipython_display_(self, **kwargs):
         return self.stream.latest().rate_limit(
             0.5).gather()._ipython_display_(**kwargs)

streamz/dataframe/core.py

@@ -326,6 +326,10 @@ def concat(tup, module=None, columns=None):
                 example = kwargs.get('example')
             elif len(args) > 1:
                 example = args[1]
+            if callable(example):
+                example = example()
+                kwargs["example"] = example
+
             self._subtype = get_base_frame_type(self.__class__.__name__,
                                                 is_dataframe_like, example)
             super(DataFrame, self).__init__(*args, **kwargs)
@@ -337,6 +341,14 @@ def verify(self, x):
             raise IndexError("Input expected to have columns %s, got %s" %
                              (self.example.columns, x.columns))
 
+    @property
+    def plot(self):
+        try:
+            import hvplot.streamz
+        except ImportError as err:  # pragma: no cover
+            raise ImportError("Streamz dataframe plotting requires hvplot") from err
+        return self.hvplot
+
 
 class _SeriesMixin(object):
     @property