"ValueError: Could not get frequency alias for plotting" if DataFrame freq attr is None #2116
Description
The following was encountered when using Pandas 0.9.0 (specifically 0.9.0ppa6revno-3341~quantal1 from pythonxy PPA):
In [50]: df = pandas.read_csv("pandas_test.csv", parse_dates={'tstamp':[0,1]}, index_col='tstamp')
In [51]: df
Out[51]:
flow
tstamp
2008-01-01 00:15:00 0.103906
2008-01-01 00:30:00 0.103906
2008-01-01 00:45:00 0.103906
2008-01-01 01:00:00 0.103906
2008-01-01 01:15:00 0.103906
2008-01-01 01:30:00 0.103906
2008-01-01 01:45:00 0.103906
2008-01-01 02:00:00 0.103906
2008-01-01 02:15:00 0.103594
In [5]: df.index
Out[5]:
<class 'pandas.tseries.index.DatetimeIndex'>
[2008-01-01 00:15:00, ..., 2008-01-01 02:15:00]
Length: 9, Freq: None, Timezone: None
In [52]: df.plot()
---------------------------------------------------------------------------
ValueError Traceback (most recent call last)
<ipython-input-52-4f76bcc16520> in <module>()
----> 1 df.plot()
/usr/lib/pymodules/python2.7/pandas/tools/plotting.pyc in plot_frame(frame, x, y, subplots, sharex, sharey, use_index, figsize, grid, legend, rot, ax, style, title, xlim, ylim, logy, xticks, yticks, kind, sort_columns, fontsize, secondary_y, **kwds)
1249 sort_columns=sort_columns, secondary_y=secondary_y,
1250 **kwds)
-> 1251 plot_obj.generate()
1252 plot_obj.draw()
1253 if subplots:
/usr/lib/pymodules/python2.7/pandas/tools/plotting.pyc in generate(self)
573 self._compute_plot_data()
574 self._setup_subplots()
--> 575 self._make_plot()
576 self._post_plot_logic()
577 self._adorn_subplots()
/usr/lib/pymodules/python2.7/pandas/tools/plotting.pyc in _make_plot(self)
880 # this is slightly deceptive
881 if self.use_index and self._use_dynamic_x():
--> 882 data = self._maybe_convert_index(self.data)
883 self._make_ts_plot(data, **self.kwds)
884 else:
/usr/lib/pymodules/python2.7/pandas/tools/plotting.pyc in _maybe_convert_index(self, data)
1022
1023 if freq is None:
-> 1024 raise ValueError('Could not get frequency alias for plotting')
1025
1026 data = DataFrame(data.values,
ValueError: Could not get frequency alias for plottingHowever:
In [7]: df2 = df.resample("15min")
In [8]: df2.plot()
Out[8]: <matplotlib.axes.AxesSubplot at 0x4be91d0>