title: Plotting time serie grouped in multiple levels
body: <p>I have a dataset with the following structure:</p>
  
  <pre><code>df = pd.read_csv('daily-minimum-values.csv', header=0, dtype={'Value':float})
  df['Date'] = df['Date'].astype('datetime64[ns]')
  df.head()
  </code></pre>
  
  
  
  <pre><code>+------------+-------+
  | Date       | Value |
  +------------+-------+
  | 1990-01-01 | 20.7  |
  +------------+-------+
  | 1990-01-02 | 17.4  |
  +------------+-------+
  | 1990-01-03 | 18.1  |
  +------------+-------+
  | 1990-01-04 | 15.6  |
  +------------+-------+
  | 1990-01-05 | 12.4  |
  +------------+-------+
  </code></pre>
  
  <p>The dataset is a time serie containing data from 1990 to 2013. I'd would like to visually analyze this time serie year to year, so I've tried to generate a figure with multiple subplots each for year, the problem is I'd also like to show quarter/month/date or date in x-axis, for example:</p>
  
  <p><a href="https://i.stack.imgur.com/vvZxf.png" rel="nofollow noreferrer">Plot example</a></p>
  
  <p>I need to generate plots for multiple levels of aggregation in x-axis, so I've tried several things.</p>
  
  <pre><code>df.groupby(pd.Grouper(key='Date', freq='A')).plot(x="Date",y="Value") # Group by year and plot date in x-axes 
  </code></pre>
  
  <p>Which returns multiple plots but it is complicated to see multiple plots at a glance for comparative purpose:</p>
  
  <p><a href="https://i.stack.imgur.com/S4bHt.png" rel="nofollow noreferrer">Generated plots</a></p>
  
  <p>I've tried adding two columns to my dataframe, for year and month expecting it is easier to plot but I dont get how matplotlib works.</p>
  
  <pre><code>df["year"]=df.Date.dt.year
  df["month"]=df.Date.dt.month
  df.groupby('year',"month")["Value"].sum().plot(x='month', y='Value')
  </code></pre>
  
  <p>Which produces the following error:</p>
  
  <blockquote>
    <p>ValueError: No axis named month for object type </p>
  </blockquote>
  
  <ul>
  <li>How do matplotlib and pandas work for this requeriment?</li>
  <li>How can I get the desired plots? </li>
  </ul>
  
  <p>Thanks in advance.</p>