title: How to separate date and time in DataFrame
body: <p>I am a beginner of Python.
  I have the dataframe <code>df_all_data_0</code> with column <code>time_in</code>:</p>
  
  <pre><code>2018-01-13 13:17:29
  2018-01-06 17:49:43
  2018-01-18 09:44:37
  2018-01-04 10:45:52
  2018-01-11 12:58:31
  </code></pre>
  
  <p>I want to separate the date (e.g., 2018-01-13) and time (13:17:29).
  What I tried:</p>
  
  <pre><code>pd.to_datetime(df_all_data_0['time_in']).
  date_str = df_all_data_0.strptime('%Y-%m-%d')
  </code></pre>
  
  <p>But I have en error:</p>
  
  <hr>
  
  <pre><code>AttributeError                            Traceback (most recent call last)
  &lt;ipython-input-14-d662eee68034&gt; in &lt;module&gt;()
        8 
        9 
  ---&gt; 10 date_str = df_all_data_0.strptime('%Y-%m-%d')
       11 #print(type(date_str)) # &lt;class 'str'&gt;
       12 #print(date_str) # 2017-10-24
  
  /anaconda/lib/python3.6/site-packages/pandas/core/generic.py in __getattr__(self, name)
     2968             if name in self._info_axis:
     2969                 return self[name]
  -&gt; 2970             return object.__getattribute__(self, name)
     2971 
     2972     def __setattr__(self, name, value):
  
  AttributeError: 'DataFrame' object has no attribute 'strptime'
  </code></pre>
  
  <p>How do it correct?</p>