title: Format datetime field as MON-YYYY in python pandas & ignore nulls
body: <p>I have a python pandas dataframe "df" as below -</p>
  
  <pre><code>      NAME  SETID   VENDOR_ID vendor_created_date
  0  Vendor1     SD          93 2002-11-22 11:04:33
  1  Vendor2     SD          94 2003-08-09 11:40:59
  2  Service1    SD          95 2003-10-31 10:29:21
  3  Vendor3     SD          01                 NaT
  4  Vendor4     SD          02                 NaT 
  </code></pre>
  
  <p>The <code>vendor_created_date</code> is of the format <code>datetime64[ns]</code>.</p>
  
  <p>Now I want to create a new field called <code>fomatted_date</code> where the <code>vendor_created_date</code> field values should be in the format <code>MON-YYYY</code> &amp; I want to delete the rows with <code>NaT</code> in the date field.</p>
  
  <p>Can you please give me directions? </p>