title: Get specific row by using SparkR
body: <p>I have a dataset "data" in SparkR of type DataFrame. 
  I want to get entry number 50 for example.
  In R I simply type <code>data[50,]</code> but when I do this in sparkR I get this message</p>
  
  <blockquote>
    <p>"Error: object of type 'S4' is not subsettable"</p>
  </blockquote>
  
  <p>What can I do to solve this ?</p>
  
  <p>Furthermore: How can I add a column (of the same column-size) to the data?</p>