[SPARK-11766][MLLIB] add toJson/fromJson to Vector/Vectors

This is to support JSON serialization of Param[Vector] in the pipeline API. It could be used for other purposes too. The schema is the same as `VectorUDT`. jkbradley

Author: Xiangrui Meng <meng@databricks.com>

Closes #9751 from mengxr/SPARK-11766.

1 files changed, 45 insertions, 0 deletions

diff --git a/mllib/src/main/scala/org/apache/spark/mllib/linalg/Vectors.scala b/mllib/src/main/scala/org/apache/spark/mllib/linalg/Vectors.scala
index bd9badc03c..4dcf351df4 100644
--- a/mllib/src/main/scala/org/apache/spark/mllib/linalg/Vectors.scala
+++ b/mllib/src/main/scala/org/apache/spark/mllib/linalg/Vectors.scala
@@ -24,6 +24,9 @@ import scala.annotation.varargs
 import scala.collection.JavaConverters._
 
 import breeze.linalg.{DenseVector => BDV, SparseVector => BSV, Vector => BV}
+import org.json4s.DefaultFormats
+import org.json4s.JsonDSL._
+import org.json4s.jackson.JsonMethods.{compact, render, parse => parseJson}
 
 import org.apache.spark.SparkException
 import org.apache.spark.annotation.{AlphaComponent, Since}
@@ -171,6 +174,12 @@ sealed trait Vector extends Serializable {
    */
   @Since("1.5.0")
   def argmax: Int
+
+  /**
+   * Converts the vector to a JSON string.
+   */
+  @Since("1.6.0")
+  def toJson: String
 }
 
 /**
@@ -339,6 +348,27 @@ object Vectors {
     parseNumeric(NumericParser.parse(s))
   }
 
+  /**
+   * Parses the JSON representation of a vector into a [[Vector]].
+   */
+  @Since("1.6.0")
+  def fromJson(json: String): Vector = {
+    implicit val formats = DefaultFormats
+    val jValue = parseJson(json)
+    (jValue \ "type").extract[Int] match {
+      case 0 => // sparse
+        val size = (jValue \ "size").extract[Int]
+        val indices = (jValue \ "indices").extract[Seq[Int]].toArray
+        val values = (jValue \ "values").extract[Seq[Double]].toArray
+        sparse(size, indices, values)
+      case 1 => // dense
+        val values = (jValue \ "values").extract[Seq[Double]].toArray
+        dense(values)
+      case _ =>
+        throw new IllegalArgumentException(s"Cannot parse $json into a vector.")
+    }
+  }
+
   private[mllib] def parseNumeric(any: Any): Vector = {
     any match {
       case values: Array[Double] =>
@@ -650,6 +680,12 @@ class DenseVector @Since("1.0.0") (
       maxIdx
     }
   }
+
+  @Since("1.6.0")
+  override def toJson: String = {
+    val jValue = ("type" -> 1) ~ ("values" -> values.toSeq)
+    compact(render(jValue))
+  }
 }
 
 @Since("1.3.0")
@@ -837,6 +873,15 @@ class SparseVector @Since("1.0.0") (
     }.unzip
     new SparseVector(selectedIndices.length, sliceInds.toArray, sliceVals.toArray)
   }
+
+  @Since("1.6.0")
+  override def toJson: String = {
+    val jValue = ("type" -> 0) ~
+      ("size" -> size) ~
+      ("indices" -> indices.toSeq) ~
+      ("values" -> values.toSeq)
+    compact(render(jValue))
+  }
 }
 
 @Since("1.3.0")