title: Sort Index by list - Python Pandas
body: <p>I have a dataframe that I have pivoted:</p>
  
  <pre><code>FinancialYear   2014/2015   2015/2016   2016/2017   2017/2018
  Month               
  April             42           32          29          27
  August            34           28          32           0
  December          45           51          28           0
  February          28           20          28           0
  January           32           28          33           0
  July              40           66          31          30
  June              32           67          37          35
  March             43           36          39           0
  May               34           30          24          29
  November          39           32          31           0
  October           38           39          28           0
  September         29           19          34           0
  </code></pre>
  
  <p>This is the code that I used:</p>
  
  <pre><code>new_hm01 = hmdf[['FinancialYear','Month','FirstReceivedDate']]
  
  hm05 = new_hm01.pivot_table(index=['FinancialYear','Month'], aggfunc='count')
  
  df_hm = new_hm01.groupby(['Month', 'FinancialYear']).size().unstack(fill_value=0).rename(columns=lambda x: '{}'.format(x))
  </code></pre>
  
  <p>The Months are not in the order I want, so I used the following code to reindex it according to a list:</p>
  
  <pre><code>vals = ['April', 'May', 'June', 'July', 'August', 'September', 'October', 'November', 'December', 'January', 'February', 'March']
  
  df_hm = df_hm.reindex(vals)
  </code></pre>
  
  <p>This worked, but the values in my table are now mostly showing <code>NaN</code> values.</p>
  
  <pre><code>FinancialYear   2014/2015   2015/2016   2016/2017   2017/2018
  Month               
  April              nan          nan         nan         nan
  May                nan          nan         nan         nan
  June               nan          nan         nan         nan
  July               nan          nan         nan         nan
  August             nan          nan         nan         nan
  September           29           19          34           0
  October            nan          nan         nan         nan
  November           nan          nan         nan         nan
  December           nan          nan         nan         nan
  January            nan          nan         nan         nan
  February           nan          nan         nan         nan
  March              nan          nan         nan         nan
  </code></pre>
  
  <p>Any idea on what is happening? How to fix it? and if there is a better alternative method?</p>