title: pivot_table() to a df no numeric types to aggregate
body: <p>I have a df which I am trying to denormalize. Basically I want to change parameter values such as, <code>'inst-cap-c'</code>, <code>'cap-lo-c'</code>, etc... into columns.</p>
  
  <p>In order to do that there were so far 2 methods within the pandas lib. With both of them I encountered some problems and were unable to denormalize this df...</p>
  
  <p>df looks like following (for simplicity used ...):</p>
  
  <pre><code>data       
     Site  Storage Commodity     parameter    value
  0  Mid   Pump    Elec         inst-cap-c        0
  1  Mid   Pump    Elec           cap-lo-c        0
  2  Mid   Pump    Elec           cap-up-c  1.5e+15
  3  Mid   Pump    Elec         inst-cap-p        0
  4  Mid   Pump    Elec           cap-lo-p        0
  ...
  52 South Pump    Elec               wacc     0.07
  53 South Pump    Elec       depreciation       50
  54 South Pump    Elec               init        1
  55 South Pump    Elec          discharge  3.5e-06
  56 South Pump    Elec           ep-ratio     None
  </code></pre>
  
  <p>When I try to create columns with parameter values via:</p>
  
  <pre><code>data.pivot_table(values='value',
                   index=['Site', 'Storage', 'Commodity'],
                   columns='parameter')
  </code></pre>
  
  <p>it simply says: <code>*** pandas.core.base.DataError: No numeric types to aggregate</code></p>
  
  <p>I am guessing it is because <code>None</code> value of <code>ep-ratio</code>, I can't use <code>NaN</code> over <code>None</code>, because it created other problems.</p>
  
  <p>So how can I denormalize this dataframe?</p>
  
  <p><strong>Expected outcome:</strong></p>
  
  <pre><code>data       
     Site    Storage  Commodity  inst-cap-c  cap-lo-c cap-up-c ... ep-ratio
  0  Mid     Pump     Elec                0         0  1.5e+15 ...     None
  1  North   Pump     Elec                0         0  1.5e+15 ...     None
  2  South   Pump     Elec                0         0  1.5e+15 ...     None
  </code></pre>
  
  <hr>
  
  <p>Extra:</p>
  
  <pre><code>data.set_index(['Site', 'Storage','Commodity'], append=True).unstack('parameter')
  *** KeyError: 'Level parameter not found'
  </code></pre>
  
  <p>I checked this also: <a href="https://stackoverflow.com/questions/39229005/pivot-table-no-numeric-types-to-aggregate?rq=1">pivot_table No numeric types to aggregate</a> it does not help</p>