title: How to get a new date from two date(hour) columns
body: <p>I have a dataframe including a datetime column for date and a column for date of change.
  Example:</p>
  <pre><code>    obdate      cdate
  0   2015-01-04  11
  0   2016-03-20  7
  0   2017-07-15  14d20h
  0   2017-12-14  12
  </code></pre>
  <p>I need a new datetime column based on the <code>cdate</code> column.
  Example:</p>
  <pre><code>    obdate      cdate     newdate
  0   2015-01-04  11        2015-01-04 11:00:00
  0   2016-03-20  7         2016-03-20 07:00:00
  0   2017-07-15  14d20h    2017-07-14 20:00:00
  0   2017-12-14  12        2017-12-14 12:00:00  
  </code></pre>
  <p>How can I do it?</p>