title: Spark: Extaract domain from email address in dataframe
body: <p>I have a difficulty in extracting email domains. I have below dataframe.</p>
  
  <pre><code>+---+----------------+
  |id |email           |
  +---+----------------+
  |1  |ii@koko.com     |
  |2  |lol@fsa.org     |
  |3  |kokojambo@mon.eu|
  +---+----------------+
  </code></pre>
  
  <p>Now I want to have a new field for domains which I'll get: </p>
  
  <pre><code>+---+----------------+------+
  |id |email           |domain|
  +---+----------------+------+
  |1  |ii@koko.com     |koko  |
  |2  |lol@fsa.org     |fsa   |
  |3  |kokojambo@mon.eu|mon   |
  +---+----------------+------+
  </code></pre>
  
  <p>I tried to do something like this:</p>
  
  <pre><code>val test = df_short.withColumn("email", split($"email", "@."))
  </code></pre>
  
  <p>But got a false output. Can anybody direct me better?</p>