title: Add rows for dataframe based on column
body: <p>I have dataframe</p>
  
  <pre><code>mydf &lt;- data.frame(userid = c("1"),gender = c("boy girl boy"), dob = c("25-Mar-2016 02-Nov-2013 12-Nov-2014") )
  </code></pre>
  
  <p>I need to add and split like this</p>
  
  <pre><code>                userid gender dob
              1      1    boy 25-Mar-2016
              2      1   girl 02-Nov-2013
              3      1    boy 12-Nov-2014
  </code></pre>
  
  <p>Any help will be greatly appreciated. Thanks</p>