title: Filter out rows with more than certain number of NaN
body: <p>In a Pandas dataframe, I would like to filter out all the rows that have more than 2 <code>NaN</code>s.</p>
  
  <p>Essentially, I have 4 columns and I would like to keep only those rows where at least 2 columns have finite values. </p>
  
  <p>Can somebody advise on how to achieve this?</p>