title: Spark: Add column to dataframe conditionally
body: <p>I am trying to take my input data:</p>
  
  <pre><code>A    B       C
  --------------
  4    blah    2
  2            3
  56   foo     3
  </code></pre>
  
  <p>And add a column to the end based on whether B is empty or not:</p>
  
  <pre><code>A    B       C     D
  --------------------
  4    blah    2     1
  2            3     0
  56   foo     3     1
  </code></pre>
  
  <p>I can do this easily by registering the input dataframe as a temp table, then typing up a SQL query.</p>
  
  <p>But I'd really like to know how to do this with just Scala methods and not having to type out a SQL query within Scala.</p>
  
  <p>I've tried <code>.withColumn</code>, but I can't get that to do what I want.</p>