title: percentage of sum in dataframe pandas
body: <p>i created the following dataframe by using pandas melt and groupby with value and variable.  I used the following:</p>
  
  <p>df2 = pd.melt(df1).groupby(['value','variable'])['variable'].count().unstack('variable').fillna(0)</p>
  
  <pre><code>         Percentile     Percentile1     Percentile2     Percentile3
  value                                               
  None          0             16              32              48
  bottom        0             69              85              88  
  top           0             69              88              82  
  mediocre     414           260             209             196 
  </code></pre>
  
  <p>I'm looking to create an output that excludes the 'None' row and creates a percentage of the sum of the 'bottom', 'top', and 'mediocre' rows. Desire output would be the following.</p>
  
  <pre><code>         Percentile     Percentile1     Percentile2     Percentile3
  value                                               
  bottom        0%          17.3%             22.3%              24.0%    
  top           0%          17.3%             23.0%              22.4%    
  mediocre     414%         65.3%             54.7%              53.6%
  </code></pre>
  
  <p>one of the main parts of this that i'm struggling with is creating a new row to equal an output.  any help would be greatly appreciated!</p>