title: Spark Scala Dataframes: Filter records which returns false for a function
body: <pre><code>dataFrame.select(columnName).filter(myFunction(_));
  </code></pre>
  
  <p>I need to filter out only those records which returns true for "myFunction";
  myFunction accepts the column value for each records, and does some analysis on the value and returns true or false. </p>
  
  <p>What I want to achieve is to filter out values which cannot be cast to numeric data (say double). I have a column which contains mostly numeric data and a few string data. I want to filter out those values which cannot be cast to double.</p>