title: value mkString is not a value of org.apache.spark.rdd.RDD[Int]
body: <p>I changed this line: </p>
  
  <pre><code>val ratedNum = rows.sortBy(- _._2).map{case (user , ratednum) =&gt; ratednum}.take(20).mkString("::")
  </code></pre>
  
  <p>to:</p>
  
  <pre><code>val ratedNum = rows.sortBy(- _._2).map{case (user , ratednum) =&gt; ratednum}.mkString("::") 
  </code></pre>
  
  <p>But Eclipse is giving me an error hint: <code>value mkString is not a value of org.apache.spark.rdd.RDD[Int]</code></p>
  
  <p>What does this error mean?</p>