rename LabelParser.apply to LabelParser.parse

use extends for singleton

Author: mengxr

mllib/src/main/scala/org/apache/spark/mllib/util/LabelParsers.scala

@@ -20,7 +20,7 @@ package org.apache.spark.mllib.util
 /** Trait for label parsers. */
 trait LabelParser extends Serializable {
   /** Parses a string label into a double label. */
-  def apply(labelString: String): Double
+  def parse(labelString: String): Double
 }
 
 /**
@@ -32,24 +32,22 @@ class BinaryLabelParser extends LabelParser {
    * Parses the input label into positive (1.0) if the value is greater than 0.5,
    * or negative (0.0) otherwise.
    */
-  override def apply(labelString: String): Double = if (labelString.toDouble > 0.5) 1.0 else 0.0
+  override def parse(labelString: String): Double = if (labelString.toDouble > 0.5) 1.0 else 0.0
 }
 
-object BinaryLabelParser {
-  private lazy val instance = new BinaryLabelParser()
+object BinaryLabelParser extends BinaryLabelParser {
   /** Gets the default instance of BinaryLabelParser. */
-  def apply(): BinaryLabelParser = instance
+  def getInstance(): BinaryLabelParser = this
 }
 
 /**
  * Label parser for multiclass labels, which converts the input label to double.
  */
 class MulticlassLabelParser extends LabelParser {
-  override def apply(labelString: String): Double =  labelString.toDouble
+  override def parse(labelString: String): Double =  labelString.toDouble
 }
 
-object MulticlassLabelParser {
-  private lazy val instance = new MulticlassLabelParser()
+object MulticlassLabelParser extends MulticlassLabelParser {
   /** Gets the default instance of MulticlassLabelParser. */
-  def apply(): MulticlassLabelParser = instance
+  def getInstance(): MulticlassLabelParser = this
 }

mllib/src/main/scala/org/apache/spark/mllib/util/MLUtils.scala

@@ -78,7 +78,7 @@ object MLUtils {
       }.reduce(math.max)
     }
     parsed.map { items =>
-      val label = labelParser(items.head)
+      val label = labelParser.parse(items.head)
       val (indices, values) = items.tail.map { item =>
         val indexAndValue = item.split(':')
         val index = indexAndValue(0).toInt - 1
@@ -96,7 +96,7 @@ object MLUtils {
    * with number of features determined automatically and the default number of partitions.
    */
   def loadLibSVMData(sc: SparkContext, path: String): RDD[LabeledPoint] =
-    loadLibSVMData(sc, path, BinaryLabelParser(), -1, sc.defaultMinSplits)
+    loadLibSVMData(sc, path, BinaryLabelParser, -1, sc.defaultMinSplits)
 
   /**
    * Loads labeled data in the LIBSVM format into an RDD[LabeledPoint],

mllib/src/test/scala/org/apache/spark/mllib/util/MLUtilsSuite.scala

@@ -80,7 +80,7 @@ class MLUtilsSuite extends FunSuite with LocalSparkContext {
     Files.write(lines, file, Charsets.US_ASCII)
     val path = tempDir.toURI.toString
 
-    val pointsWithNumFeatures = MLUtils.loadLibSVMData(sc, path, BinaryLabelParser(), 6).collect()
+    val pointsWithNumFeatures = MLUtils.loadLibSVMData(sc, path, BinaryLabelParser, 6).collect()
     val pointsWithoutNumFeatures = MLUtils.loadLibSVMData(sc, path).collect()
 
     for (points <- Seq(pointsWithNumFeatures, pointsWithoutNumFeatures)) {
@@ -93,7 +93,7 @@ class MLUtilsSuite extends FunSuite with LocalSparkContext {
       assert(points(2).features === Vectors.sparse(6, Seq((1, 4.0), (3, 5.0), (5, 6.0))))
     }
 
-    val multiclassPoints = MLUtils.loadLibSVMData(sc, path, MulticlassLabelParser()).collect()
+    val multiclassPoints = MLUtils.loadLibSVMData(sc, path, MulticlassLabelParser).collect()
     assert(multiclassPoints.length === 3)
     assert(multiclassPoints(0).label === 1.0)
     assert(multiclassPoints(1).label === -1.0)