title: What are DecisionTree.trainClassifier parameters in Spark
body: <p>I'm studying Spark MLlib.
  While studying DecisionTree, I see following DecisionTree.trainClassifier usage example.</p>
  
  <p></p>
  
  <pre><code>import org.apache.spark.mllib.tree._
  val model = DecisionTree.trainClassifier(trainData, 7, Map[int, int](), "gini", 4, 100)
  </code></pre>
  
  <p>There are 6 parameters here, I don't understand the 3rd(Map), 5th(4) and 6th(100) parameters.</p>
  
  <p>Google says they are categorical feature, lambda and alpha.
  Can anyone explain them a bit better?</p>
  
  <p>need your kind help</p>