title: Python Dataframe extract last reading of the day for many days
body: <p>My dataframe has many timestamps on a given day and many days of the data of the year. I want to extract last reading of the day and store it in a new dataframe. </p>
  
  <pre><code>df = 
  
  datetime                     A
  01/24/2019 08:27:00 AM    0.905434
  01/24/2019 08:28:00 AM    0.913460
  01/24/2019 08:29:00 AM    0.926724
  01/25/2019 08:30:00 AM    0.937575
  01/25/2019 08:31:00 AM    0.946422
  01/25/2019 08:32:00 AM    0.951792
  01/26/2019 08:33:00 AM    0.957930
  01/26/2019 08:34:00 AM    0.963631
  01/26/2019 08:35:00 AM    0.968414
  01/26/2019 08:36:00 AM    0.972460
  </code></pre>
  
  <p>My code: </p>
  
  <pre><code> aux = []
   for i in df.index.strftime("%Y-%m-%d").unique():
       auxdf = df.loc[i]
       aux.append(auxdf.iloc[-1])
  </code></pre>
  
  <p>It is not working. </p>