title: From RangeIndex to DatetimeIndex
body: <p>I am analyzing the time series of an action (historical from 2000 to 2018). I
  want to be able to better analyze my time series (e.g. on a monthly, quarterly basis) by placing all the datetime data in a
  DatetimeIndex. How can I do it? Is it possible?</p>
  
  <pre><code>df.columns
  Out[181]: Index(['Date', 'Price', 'Open', 'High', 'Low'], dtype='object')
  
  df.index
  Out[179]: RangeIndex(start=0, stop=4309, step=1)
  
  df.info
  [4309 rows x 5 columns]&gt;
  
  type(df)
  Out[178]: pandas.core.frame.DataFrame
  </code></pre>