[SPARK-10023] [ML] [PySpark] Unified DecisionTreeParams checkpointInterval between Scala and Python API.

"checkpointInterval" is member of DecisionTreeParams in Scala API which is inconsistency with Python API, we should unified them.
```
member of DecisionTreeParams <-> Scala API
shared param for all ML Transformer/Estimator <-> Python API
```
Proposal:
"checkpointInterval" is also used by ALS, so we make it shared params at Scala.

Author: Yanbo Liang <ybliang8@gmail.com>

Closes #8528 from yanboliang/spark-10023.

4 files changed, 16 insertions, 24 deletions

diff --git a/mllib/src/main/scala/org/apache/spark/ml/classification/DecisionTreeClassifier.scala b/mllib/src/main/scala/org/apache/spark/ml/classification/DecisionTreeClassifier.scala
index 6f70b96b17..0a75d5d222 100644
--- a/mllib/src/main/scala/org/apache/spark/ml/classification/DecisionTreeClassifier.scala
+++ b/mllib/src/main/scala/org/apache/spark/ml/classification/DecisionTreeClassifier.scala
@@ -19,6 +19,7 @@ package org.apache.spark.ml.classification
 
 import org.apache.spark.annotation.Experimental
 import org.apache.spark.ml.param.ParamMap
+import org.apache.spark.ml.param.shared.HasCheckpointInterval
 import org.apache.spark.ml.tree.{DecisionTreeModel, DecisionTreeParams, Node, TreeClassifierParams}
 import org.apache.spark.ml.tree.impl.RandomForest
 import org.apache.spark.ml.util.{Identifiable, MetadataUtils}
diff --git a/mllib/src/main/scala/org/apache/spark/ml/param/shared/SharedParamsCodeGen.scala b/mllib/src/main/scala/org/apache/spark/ml/param/shared/SharedParamsCodeGen.scala
index 8c16c6149b..e9e99ed1db 100644
--- a/mllib/src/main/scala/org/apache/spark/ml/param/shared/SharedParamsCodeGen.scala
+++ b/mllib/src/main/scala/org/apache/spark/ml/param/shared/SharedParamsCodeGen.scala
@@ -56,7 +56,8 @@ private[shared] object SharedParamsCodeGen {
       ParamDesc[String]("inputCol", "input column name"),
       ParamDesc[Array[String]]("inputCols", "input column names"),
       ParamDesc[String]("outputCol", "output column name", Some("uid + \"__output\"")),
-      ParamDesc[Int]("checkpointInterval", "checkpoint interval (>= 1)",
+      ParamDesc[Int]("checkpointInterval", "checkpoint interval (>= 1). E.g. 10 means that " +
+        "the cache will get checkpointed every 10 iterations.",
         isValid = "ParamValidators.gtEq(1)"),
       ParamDesc[Boolean]("fitIntercept", "whether to fit an intercept term", Some("true")),
       ParamDesc[String]("handleInvalid", "how to handle invalid entries. Options are skip (which " +
diff --git a/mllib/src/main/scala/org/apache/spark/ml/param/shared/sharedParams.scala b/mllib/src/main/scala/org/apache/spark/ml/param/shared/sharedParams.scala
index c26768953e..3009217086 100644
--- a/mllib/src/main/scala/org/apache/spark/ml/param/shared/sharedParams.scala
+++ b/mllib/src/main/scala/org/apache/spark/ml/param/shared/sharedParams.scala
@@ -223,10 +223,10 @@ private[ml] trait HasOutputCol extends Params {
 private[ml] trait HasCheckpointInterval extends Params {
 
   /**
-   * Param for checkpoint interval (>= 1).
+   * Param for checkpoint interval (>= 1). E.g. 10 means that the cache will get checkpointed every 10 iterations..
    * @group param
    */
-  final val checkpointInterval: IntParam = new IntParam(this, "checkpointInterval", "checkpoint interval (>= 1)", ParamValidators.gtEq(1))
+  final val checkpointInterval: IntParam = new IntParam(this, "checkpointInterval", "checkpoint interval (>= 1). E.g. 10 means that the cache will get checkpointed every 10 iterations.", ParamValidators.gtEq(1))
 
   /** @group getParam */
   final def getCheckpointInterval: Int = $(checkpointInterval)
diff --git a/mllib/src/main/scala/org/apache/spark/ml/tree/treeParams.scala b/mllib/src/main/scala/org/apache/spark/ml/tree/treeParams.scala
index dbd8d31571..d29f5253c9 100644
--- a/mllib/src/main/scala/org/apache/spark/ml/tree/treeParams.scala
+++ b/mllib/src/main/scala/org/apache/spark/ml/tree/treeParams.scala
@@ -20,7 +20,7 @@ package org.apache.spark.ml.tree
 import org.apache.spark.ml.classification.ClassifierParams
 import org.apache.spark.ml.PredictorParams
 import org.apache.spark.ml.param._
-import org.apache.spark.ml.param.shared.{HasMaxIter, HasSeed, HasThresholds}
+import org.apache.spark.ml.param.shared.{HasCheckpointInterval, HasMaxIter, HasSeed, HasThresholds}
 import org.apache.spark.mllib.tree.configuration.{Algo => OldAlgo, BoostingStrategy => OldBoostingStrategy, Strategy => OldStrategy}
 import org.apache.spark.mllib.tree.impurity.{Entropy => OldEntropy, Gini => OldGini, Impurity => OldImpurity, Variance => OldVariance}
 import org.apache.spark.mllib.tree.loss.{Loss => OldLoss}
@@ -30,7 +30,7 @@ import org.apache.spark.mllib.tree.loss.{Loss => OldLoss}
  *
  * Note: Marked as private and DeveloperApi since this may be made public in the future.
  */
-private[ml] trait DecisionTreeParams extends PredictorParams {
+private[ml] trait DecisionTreeParams extends PredictorParams with HasCheckpointInterval {
 
   /**
    * Maximum depth of the tree (>= 0).
@@ -96,21 +96,6 @@ private[ml] trait DecisionTreeParams extends PredictorParams {
     " algorithm will cache node IDs for each instance. Caching can speed up training of deeper" +
     " trees.")
 
-  /**
-   * Specifies how often to checkpoint the cached node IDs.
-   * E.g. 10 means that the cache will get checkpointed every 10 iterations.
-   * This is only used if cacheNodeIds is true and if the checkpoint directory is set in
-   * [[org.apache.spark.SparkContext]].
-   * Must be >= 1.
-   * (default = 10)
-   * @group expertParam
-   */
-  final val checkpointInterval: IntParam = new IntParam(this, "checkpointInterval", "Specifies" +
-    " how often to checkpoint the cached node IDs.  E.g. 10 means that the cache will get" +
-    " checkpointed every 10 iterations. This is only used if cacheNodeIds is true and if the" +
-    " checkpoint directory is set in the SparkContext. Must be >= 1.",
-    ParamValidators.gtEq(1))
-
   setDefault(maxDepth -> 5, maxBins -> 32, minInstancesPerNode -> 1, minInfoGain -> 0.0,
     maxMemoryInMB -> 256, cacheNodeIds -> false, checkpointInterval -> 10)
 
@@ -150,12 +135,17 @@ private[ml] trait DecisionTreeParams extends PredictorParams {
   /** @group expertGetParam */
   final def getCacheNodeIds: Boolean = $(cacheNodeIds)
 
-  /** @group expertSetParam */
+  /**
+   * Specifies how often to checkpoint the cached node IDs.
+   * E.g. 10 means that the cache will get checkpointed every 10 iterations.
+   * This is only used if cacheNodeIds is true and if the checkpoint directory is set in
+   * [[org.apache.spark.SparkContext]].
+   * Must be >= 1.
+   * (default = 10)
+   * @group expertSetParam
+   */
   def setCheckpointInterval(value: Int): this.type = set(checkpointInterval, value)
 
-  /** @group expertGetParam */
-  final def getCheckpointInterval: Int = $(checkpointInterval)
-
   /** (private[ml]) Create a Strategy instance to use with the old API. */
   private[ml] def getOldStrategy(
       categoricalFeatures: Map[Int, Int],