title: How to convert Scala RDD to Map
body: <p>I have a RDD (array of String) <code>org.apache.spark.rdd.RDD[String] = MappedRDD[18]</code>
  and to convert it to a map with unique Ids. I did '<code>val vertexMAp = vertices.zipWithUniqueId</code>'
  but this gave me another RDD of type <code>'org.apache.spark.rdd.RDD[(String, Long)]'</code> but I want a '<code>Map[String, Long]</code>' . How can I convert my '<code>org.apache.spark.rdd.RDD[(String, Long)] to Map[String, Long]</code>' ?</p>
  
  <p>Thanks</p>