title: how to make a pandas dataframe column into a datetime object showing just the date to correctly sort
body: <p>When I sort on month_date in dataframe (df) which contains </p>
  
  <p>[2014-06-01, 2014-07-01, 2014-08-01,2014-09-01,2014-10-01] I get the following:</p>
  
  <pre><code>result = df.sort(['month_date'], ascending=True) 
  </code></pre>
  
  <p>However the result is (in this order):</p>
  
  <p>10,
  6, 
  7, 
  8, 
  9,</p>
  
  <p>Whereas I expected 6, 7, 8, 9, 10  </p>
  
  <p>Maybe this is because I didn't specify that the month_date column should be a datetime object (and contain only the date and no time component.</p>
  
  <p>How do I make the month_date column in my dataframe into a datetime object which only contains the date which pandas understands so it is sorted in the following order:
  6, 
  7, 
  8, 
  9, 
  10,</p>
  
  <p><strong>UPDATE - YS-L correct answer below</strong></p>
  
  <pre><code>df = pd.DataFrame({'month_date': ['2014-06-01', '2014-01-01', '2014-08-01','2014-09-01','2014-10-01']})
  df['month_date'] = pd.to_datetime(df['month_date'])
  print df.sort(['month_date'], ascending=True)
  </code></pre>