title: Difference between dates between corresponding rows in pandas dataframe
body: <p>Below is the example of a sample pandas dataframe. I am trying to find the difference between the dates in the two rows (with the first row as the base):</p>
  
  <pre><code>PH_number   date        Type
  H09879721   2018-05-01  AccountHolder
  H09879731   2018-06-22  AccountHolder
  </code></pre>
  
  <p>If the difference between two dates is within 90 days, then those two rows should be added to a new pandas dataframe. The <code>date</code> column is of type <code>object</code>.</p>
  
  <p>How can I do this?</p>