title: python plot several curves from dataframe
body: <p>I am trying to plot several appliances' temperatures on a plot.</p>
  
  <p>The data comes from the dataframe df below, and I first create the date column as the index.</p>
  
  <pre><code>df=df.set_index('Date')
  
  Date                  Appliance      Value (degrees)
  2016-07-05 03:00:00   Thermometer    22
  2016-08-06 16:00:00   Thermometer .  19
  2016-12-07 21:00:00 . Thermometer .  25
  2016-19-08 23:00:00 . Thermostat .   21
  2016-25-09 06:00:00 . Thermostat .   20
  2016-12-10 21:00:00 . Thermometer .  18
  2016-10-11 21:00:00 . Thermostat .   21
  2016-10-12 04:00:00 . Thermometer .  20
  2017-01-01 07:00:00 . Thermostat .   19
  2017-01-02 07:00:00 . Thermometer .  23
  </code></pre>
  
  <p>We want to be able to show 2 curves: one for the thermometer's temperatures and one for the thermostat's temperatures with 2 different colours, over time.</p>
  
  <pre><code>plt.plot(df.index, [df.value for i in range(len(appliance)]
  ax = df.plot()
  ax.set_xlim(pd.Timestamp('2016-07-05'), pd.Timestamp('2015-11-30'))
  </code></pre>
  
  <p>Is ggplot better for this? </p>
  
  <p>I cannot manage to make this works</p>