title: How do I sort a pandas data frame by date time
body: <p>I have a .csv file that I am reading into a pandas data frame.  The .csv file has the following format</p>
  
  <pre><code>Date,Expense
  03/05/2015,75.0
  01/01/2015,45.0
  01/02/2015,245.0
  01/02/2015,1280.0
  01/02/2015,75.0
  01/05/2015,55.0
  01/03/2015,287.0
  01/07/2015,3185.0
  01/07/2015,981.0
  01/07/2015,342.0
  01/02/2015,64.8
  </code></pre>
  
  <p>I am reading the file in with the following code;</p>
  
  <pre><code>import pandas as pd
  df = pd.read_csv(text_file.csv, sep=',', dtype={'Date': str, 'Expense': float})
  </code></pre>
  
  <p>I then transform <code>df['Date']</code> to a date time object via;</p>
  
  <pre><code>df['Date'] = pd.to_datetime(df.Date)
  df.sort_values(by='Date')
  print(df['Date'])
  </code></pre>
  
  <p>When I print the newly sorted data it is obvious that the values were transformed into a date time object, but they are not sorted.  How do I get pandas to sort the dates in chronological order?</p>
  
  <pre><code>0  2015-03-05
  1  2015-01-01
  2  2015-01-02
  3  2015-01-02
  4  2015-01-02
  5  2015-01-05
  6  2015-01-03
  7  2015-01-07
  8  2015-01-07
  9  2015-01-07
  10 2015-01-02
  Name: Date, type: datetime64[ns]
  </code></pre>