title: Spark DataFrame aggregate multiple column into one column as a string
body: <p>I want to convert a Spark DataFrame into another DataFrame with a specific manner as follows:</p>
  
  <p>I have Spark DataFrame:</p>
  
  <pre><code>+---------+------------+
  |protocol |   count    |
  +---------+------------+
  |      TCP|    8231    |
  |     ICMP|    7314    |
  |      UDP|    5523    |
  |     IGMP|    4423    |
  |      EGP|    2331    |
  +---------+------------+
  </code></pre>
  
  <p>And I want to turn it into:</p>
  
  <pre><code>+----------------------------------------------------------+
  |Aggregated                                                |
  +----------------------------------------------------------+
  |{tcp: 8231, icmp: 7314, udp: 5523, igmp: 4423, egp: 2331} |
  +----------------------------------------------------------+
  </code></pre>
  
  <p>The aggregated column can be both list or map, or string. Is this possible with DataFrame functions or do I need to create my own udf to aggregate this ?</p>