title: Pandas convert date format
body: <p>My current date column is in the format YYYY-MM-DD but I need it in the format YYYY-MM-DD HH:MM:SS</p>
  
  <pre><code>&gt;&gt;&gt; df['Year_Month_Day'].head()
  0   2014-09-17
  1   2014-09-17
  2   2014-09-07
  3   2014-09-14
  4   2014-09-17
  Name: Year_Month_Day, dtype: datetime64[ns]
  </code></pre>
  
  <p>I tried to use pd.to_datetime to do this:</p>
  
  <pre><code>&gt;&gt;&gt; pd.to_datetime(df['Year_Month_Day'])
  0    2014-09-17
  1    2014-09-17
  2    2014-09-07
  3    2014-09-14
  4    2014-09-17
  </code></pre>
  
  <p>But no luck..</p>