title: How to join a pandas data frame with a PeriodIndex
body: <pre><code>df.index = df.index.to_period('Q')
  
  if comb.empty:
      comp = df
  else:
      comp = comp.join(df,how = 'outer')
  </code></pre>
  
  <p>When I do this I get: join() got an unexpected keyword argument 'sort' </p>
  
  <p>This is what my original dataframe looks like. I am attempting to >change it to a quarter based PeriodIndex and then join it with another dataframe with the same type of PeriodIndex. Can anyone tell my why I keep getting this error?</p>
  
  <p><a href="https://i.stack.imgur.com/G0Gev.png" rel="nofollow noreferrer">df dataframe</a></p>