title: Compare dataframe date columns and return new column
body: <p>I have a data-frame <code>df</code> comprising of an identifier column and 4 columns of dates. Please see below for the head of the data-frame.</p>
  <pre><code>   Identifier                    A \
  0       12253  1989-11-09 00:00:00   
  1       11413  1990-09-03 00:00:00   
  2       12337  1977-09-07 00:00:00   
  3       10610  1994-08-24 00:00:00   
  4        7493  1993-08-22 00:00:00   
  
                        B                              C  \
  0   2012-03-01 00:00:00            2015-04-01 00:00:00   
  1   2009-08-16 00:00:00            2015-05-18 00:00:00   
  2   1977-09-07 00:00:00            1977-09-07 00:00:00   
  3   2009-01-09 00:00:00            2015-03-01 00:00:00   
  4   2002-06-03 00:00:00            2015-02-16 00:00:00   
  
                        D  \
  0   2012-01-03 00:00:00   
  1   2015-05-18 00:00:00   
  2   1977-09-07 00:00:00   
  3   2015-03-01 00:00:00   
  4   2015-02-16 00:00:00 
  </code></pre>
  <p>I am trying to compare the date columns against each other and where if A&gt;=B&gt;=C&gt;=D then in a new column check True should be returned else False.</p>
  <p>So the resulting data-frame would look like:</p>
  <pre><code>   Identifier                    A \
  0       12253  1989-11-09 00:00:00   
  1       11413  1990-09-03 00:00:00   
  2       12337  1977-09-07 00:00:00   
  3       10610  1994-08-24 00:00:00   
  4        7493  1993-08-22 00:00:00   
  
                        B                              C  \
  0   2012-03-01 00:00:00            2015-04-01 00:00:00   
  1   2009-08-16 00:00:00            2015-05-18 00:00:00   
  2   1977-09-07 00:00:00            1977-09-07 00:00:00   
  3   2009-01-09 00:00:00            2015-03-01 00:00:00   
  4   2002-06-03 00:00:00            2015-02-16 00:00:00   
  
                        D       Check\
  0   2012-01-03 00:00:00       False
  1   2015-05-18 00:00:00       True
  2   1977-09-07 00:00:00       True 
  3   2015-03-01 00:00:00       True
  4   2015-02-16 00:00:00       True
  </code></pre>
  <p>I have tried</p>
  <pre><code>df['Check'] = np.where(df['A'] &gt;= df['B']&gt;= df['C']&gt;= df['D'], 'True', 'False')
  </code></pre>
  <p>But can't get this to work. What can I try next?</p>