title: Spark: subtract two DataFrames
body: <p>In Spark version <em>1.2.0</em> one could use <code>subtract</code> with 2 <code>SchemRDD</code>s to end up with only the different content from the first one</p>
  
  <pre><code>val onlyNewData = todaySchemaRDD.subtract(yesterdaySchemaRDD)
  </code></pre>
  
  <p><code>onlyNewData</code> contains the rows in <code>todaySchemRDD</code> that do not exist in <code>yesterdaySchemaRDD</code>.</p>
  
  <p>How can this be achieved with <code>DataFrames</code> in Spark version <em>1.3.0</em>?</p>