title: Panda Pivot Table: calculate percentage with respect to two columns
body: <p>I want to calculate the percentage with respect to 2 columns in a dataframe. The data frame is:</p>
  
  <pre><code>df1.head()
       ssaname      ym  tch_block  call_drop  cell_name
  0  AAAAAAAAA  201504          0         39        345
  1  aaaaaaaaa  201505          2         48        291
  2  bbbbbbbbb  201506          2         49        360
  3  ccccccccc  201507          4         59        357
  4  ddddddddd  201508         10         74        363
  </code></pre>
  
  <p>The percentage should be <code>tch_block*100/cell_name</code><br>
  The command tried is:   </p>
  
  <pre><code>pd.pivot_table(df1,index=['ssaname'],columns=['ym'],values=['tch_block','cell_drop'],aggfunc = lamdba x:x*100/'cell_name')
  </code></pre>