Pandas plot from csv data fails

Question

I am trying to scatter plot some data from a csv file in Pandas, but I get an error.

The input file looks like this:

time,SPOT
2016-02-04 16:01:10.785000,3.6729
2016-02-04 16:01:11,4.2344

And the code I am using to plot:

import pandas as pd
df = pd.read_csv('file.csv')
df.plot(kind='scatter', x='time', y='SPOT')

I then get this error:

    Traceback (most recent call last):
      File "C:\installed\Python27\lib\site-packages\IPython\core\interactiveshell.py", line 3066, in run_code
        exec(code_obj, self.user_global_ns, self.user_ns)
      File "<ipython-input-51-ff49e6461746>", line 1, in <module>
        df.plot(kind='scatter', x='time', y='SPOT')
      File "C:\installed\Python27\lib\site-packages\pandas\tools\plotting.py", line 2477, in plot_frame
        **kwds)
      File "C:\installed\Python27\lib\site-packages\pandas\tools\plotting.py", line 2317, in _plot
        plot_obj.generate()
      File "C:\installed\Python27\lib\site-packages\pandas\tools\plotting.py", line 923, in generate
        self._make_plot()
      File "C:\installed\Python27\lib\site-packages\pandas\tools\plotting.py", line 1445, in _make_plot
        scatter = ax.scatter(data[x].values, data[y].values, c=c_values,
      File "C:\installed\Python27\lib\site-packages\pandas\core\frame.py", line 1780, in __getitem__
        return self._getitem_column(key)
      File "C:\installed\Python27\lib\site-packages\pandas\core\frame.py", line 1787, in _getitem_column
        return self._get_item_cache(key)
      File "C:\installed\Python27\lib\site-packages\pandas\core\generic.py", line 1068, in _get_item_cache
        values = self._data.get(item)
      File "C:\installed\Python27\lib\site-packages\pandas\core\internals.py", line 2849, in get
        loc = self.items.get_loc(item)
      File "C:\installed\Python27\lib\site-packages\pandas\core\index.py", line 1402, in get_loc
        return self._engine.get_loc(_values_from_object(key))
      File "pandas\index.pyx", line 134, in pandas.index.IndexEngine.get_loc (pandas\index.c:3807)
      File "pandas\index.pyx", line 154, in pandas.index.IndexEngine.get_loc (pandas\index.c:3687)
      File "pandas\hashtable.pyx", line 696, in pandas.hashtable.PyObjectHashTable.get_item (pandas\hashtable.c:12310)
      File "pandas\hashtable.pyx", line 704, in pandas.hashtable.PyObjectHashTable.get_item (pandas\hashtable.c:12261)
KeyError: 'time'

Q1. I am wondering if my time series are not allowed to contain milliseconds in the time column?

Q2. Sometimes the times in column two have no milliseconds, presumable when it is zero. I tried to add a date_parser but it does not help.

date_parser = lambda x: pd.datetime.strptime(x, '%Y-%m-%d %H:%M:%S.%f')
df = pd.read_csv('file.csv', date_parser=date_parser)

I am using this python version 2.7.10 (default, May 23 2015, 09:40:32) [MSC v.1500 32 bit (Intel)]'

and pandas 0.15.2

Scatter doesn't work with datetime values. See github.com/pydata/pandas/issues/8113. — TomAugspurger
– TomAugspurger, Commented Feb 9, 2016 at 17:33
Thank you. Is there some kind of workaround? For example convert dates to a double? — Damian
– Damian, Commented Feb 9, 2016 at 17:38

Andy · Accepted Answer · 2016-02-09 17:54:28Z

3

The scatter plot doesn't work with datetime values. But, you can work around this, by doing a regular line graph and setting the style to .

df.plot(x='time', y='SPOT', style='.')

Mocking up some more data, I get a plot like this (you'll need to mess with the label styles, but you can get the idea of how it plots):

edited Feb 9, 2016 at 17:54

answered Feb 9, 2016 at 17:41

Andy♦

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