[SPARK-7380] [MLLIB] pipeline stages should be copyable in Python

This PR makes pipeline stages in Python copyable and hence simplifies some implementations. It also includes the following changes:

1. Rename `paramMap` and `defaultParamMap` to `_paramMap` and `_defaultParamMap`, respectively.
2. Accept a list of param maps in `fit`.
3. Use parent uid and name to identify param.

jkbradley

Author: Xiangrui Meng <meng@databricks.com>
Author: Joseph K. Bradley <joseph@databricks.com>

Closes #6088 from mengxr/SPARK-7380 and squashes the following commits:

413c463 [Xiangrui Meng] remove unnecessary doc
4159f35 [Xiangrui Meng] Merge remote-tracking branch 'apache/master' into SPARK-7380
611c719 [Xiangrui Meng] fix python style
68862b8 [Xiangrui Meng] update _java_obj initialization
927ad19 [Xiangrui Meng] fix ml/tests.py
0138fc3 [Xiangrui Meng] update feature transformers and fix a bug in RegexTokenizer
9ca44fb [Xiangrui Meng] simplify Java wrappers and add tests
c7d84ef [Xiangrui Meng] update ml/tests.py to test copy params
7e0d27f [Xiangrui Meng] merge master
46840fb [Xiangrui Meng] update wrappers
b6db1ed [Xiangrui Meng] update all self.paramMap to self._paramMap
46cb6ed [Xiangrui Meng] merge master
a163413 [Xiangrui Meng] fix style
1042e80 [Xiangrui Meng] Merge remote-tracking branch 'apache/master' into SPARK-7380
9630eae [Xiangrui Meng] fix Identifiable._randomUID
13bd70a [Xiangrui Meng] update ml/tests.py
64a536c [Xiangrui Meng] use _fit/_transform/_evaluate to simplify the impl
02abf13 [Xiangrui Meng] Merge remote-tracking branch 'apache/master' into copyable-python
66ce18c [Joseph K. Bradley] some cleanups before sending to Xiangrui
7431272 [Joseph K. Bradley] Rebased with master

3 files changed, 8 insertions, 7 deletions

diff --git a/mllib/src/main/scala/org/apache/spark/ml/feature/Tokenizer.scala b/mllib/src/main/scala/org/apache/spark/ml/feature/Tokenizer.scala
index 36d9e17eca..3f7f4f96fc 100644
--- a/mllib/src/main/scala/org/apache/spark/ml/feature/Tokenizer.scala
+++ b/mllib/src/main/scala/org/apache/spark/ml/feature/Tokenizer.scala
@@ -61,7 +61,7 @@ class RegexTokenizer(override val uid: String)
    * Default: 1, to avoid returning empty strings
    * @group param
    */
-  val minTokenLength: IntParam = new IntParam(this, "minLength", "minimum token length (>= 0)",
+  val minTokenLength: IntParam = new IntParam(this, "minTokenLength", "minimum token length (>= 0)",
     ParamValidators.gtEq(0))
 
   /** @group setParam */
diff --git a/mllib/src/main/scala/org/apache/spark/ml/param/params.scala b/mllib/src/main/scala/org/apache/spark/ml/param/params.scala
index 247e08be1b..c33b66d31c 100644
--- a/mllib/src/main/scala/org/apache/spark/ml/param/params.scala
+++ b/mllib/src/main/scala/org/apache/spark/ml/param/params.scala
@@ -483,16 +483,15 @@ trait Params extends Identifiable with Serializable {
   def copy(extra: ParamMap): Params = {
     val that = this.getClass.getConstructor(classOf[String]).newInstance(uid)
     copyValues(that, extra)
-    that
   }
 
   /**
    * Extracts the embedded default param values and user-supplied values, and then merges them with
    * extra values from input into a flat param map, where the latter value is used if there exist
-   * conflicts, i.e., with ordering: default param values < user-supplied values < extraParamMap.
+   * conflicts, i.e., with ordering: default param values < user-supplied values < extra.
    */
-  final def extractParamMap(extraParamMap: ParamMap): ParamMap = {
-    defaultParamMap ++ paramMap ++ extraParamMap
+  final def extractParamMap(extra: ParamMap): ParamMap = {
+    defaultParamMap ++ paramMap ++ extra
   }
 
   /**
diff --git a/mllib/src/main/scala/org/apache/spark/ml/util/Identifiable.scala b/mllib/src/main/scala/org/apache/spark/ml/util/Identifiable.scala
index 1466976800..ddd34a5450 100644
--- a/mllib/src/main/scala/org/apache/spark/ml/util/Identifiable.scala
+++ b/mllib/src/main/scala/org/apache/spark/ml/util/Identifiable.scala
@@ -23,15 +23,17 @@ import java.util.UUID
 /**
  * Trait for an object with an immutable unique ID that identifies itself and its derivatives.
  */
-trait Identifiable {
+private[spark] trait Identifiable {
 
   /**
    * An immutable unique ID for the object and its derivatives.
    */
   val uid: String
+
+  override def toString: String = uid
 }
 
-object Identifiable {
+private[spark] object Identifiable {
 
   /**
    * Returns a random UID that concatenates the given prefix, "_", and 12 random hex chars.