title: How can I do a contour plot with date and time in the x-y axis?
body: <p>I have some data that looks like this:</p>
  
  <pre><code>#date       time        temp    press    rh
  09/10/2011 07:50        11.4    798.1   14.1
  09/10/2011 08:00        11.9    798.3   13.6
  ...
  09/10/2011 11:30        FALSE   FALSE   FALSE
  09/10/2011 11:40        25.4    798.3   11.2
  09/10/2011 11:50        23.2    799.1   11.2
  .....
  </code></pre>
  
  <p>I want to do a contour plot of "temp" with the "time" in the x-axis and "date" in the y-axis. </p>
  
  <p>I tried using Pandas to handle the dates and the <code>NaN</code> values better. </p>
  
  <pre><code>data=np.genfromtxt("dataFile.txt", comments="#", dtype='str')
  
  header_names=['date', 'time', 'temp', 'press', 'rh']
  df = pd.DataFrame(data, dtype=None, columns=header_names) 
  df['date']=pd.to_datetime(df['date'], format='%d/%m/%Y').dt.date   
  df.time=pd.to_datetime(df.time, format='%H:%M').dt.time
  df.temp = pd.to_numeric(df.temp, errors='coerse')
  ....
  
  dfMesh=df.pivot('date', 'time', 'temp')
  X=dfMesh.columns.values
  Y=dfMesh.index.values
  Z=dfMesh.values
  
  x,y=np.meshgrid(X, Y)
  plt.contourf(x, y, Z)
  </code></pre>
  
  <p>But I get the following error: </p>
  
  <blockquote>
    <p>Traceback (most recent call last):
          File "./contourPlot_pandas.py", line 33, in 
          x,y=np.meshgrid(X, Y)
          File "/Users/marybau/anaconda/lib/python3.6/site-packages/numpy/lib/function_base.py",
    line 4533, in meshgrid
            return [x * mult_fact for x in output]
          File "/Users/marybau/anaconda/lib/python3.6/site-packages/numpy/lib/function_base.py",
    line 4533, in 
            return [x * mult_fact for x in output]
        TypeError: unsupported operand type(s) for *: 'datetime.time' and 'int</p>
  </blockquote>
  
  <p>'</p>
  
  <p>I have also tried different other ways to do it without using pandas, but I end up with similar problems due to the <code>date-time</code> format or the <code>NaN</code>. Any suggestions? Thanks!</p>