[SPARK-5573][SQL] Add explode to dataframes

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/generators.scala

@@ -73,6 +73,25 @@ abstract class Generator extends Expression {
   }
 }
 
+/**
+ * A generator that produces its output using the provided lambda function.
+ */
+case class UserDefinedGenerator(
+    schema: Seq[Attribute],
+    function: Row => TraversableOnce[Row],
+    children: Seq[Expression])
+  extends Generator{
+
+  override protected def makeOutput(): Seq[Attribute] = schema
+
+  override def eval(input: Row): TraversableOnce[Row] = {
+    val inputRow = new InterpretedProjection(children)
+    function(inputRow(input))
+  }
+
+  override def toString = s"UserDefinedGenerator(${children.mkString(",")})"
+}
+
 /**
  * Given an input array produces a sequence of rows for each value in the array.
  */

sql/core/src/main/scala/org/apache/spark/sql/DataFrame.scala

@@ -19,6 +19,7 @@ package org.apache.spark.sql
 
 import scala.collection.JavaConversions._
 import scala.reflect.ClassTag
+import scala.reflect.runtime.universe.TypeTag
 import scala.util.control.NonFatal
 
 import org.apache.spark.annotation.{DeveloperApi, Experimental}
@@ -458,6 +459,28 @@ trait DataFrame extends RDDApi[Row] {
     sample(withReplacement, fraction, Utils.random.nextLong)
   }
 
+  /**
+   * (Scala-specific) Returns a new [[DataFrame]] where each row has been expanded to zero or more
+   * rows by the provided function.  This is similar to a `LATERAL VIEW` in HiveQL.  The columns of
+   * the input row are implicitly joined with each row that is output by the function.
+   *
+   * The following example uses this function to count the number of books which contain
+   * a given word:
+   *
+   * {{{
+   *   case class Book(title: String, words: String)
+   *   val df: RDD[Book]
+   *
+   *   case class Word(word: String)
+   *   val allWords = df.explode('words) {
+   *     case Row(words: String) => words.split(" ").map(Word(_))
+   *   }
+   *
+   *   val bookCountPerWord = allWords.groupBy("word").agg(countDistinct("title"))
+   * }}}
+   */
+  def explode[A <: Product : TypeTag](input: Column*)(f: Row => TraversableOnce[A]): DataFrame
+
   /////////////////////////////////////////////////////////////////////////////
 
   /**

sql/core/src/main/scala/org/apache/spark/sql/DataFrameImpl.scala

@@ -21,6 +21,7 @@ import java.io.CharArrayWriter
 
 import scala.language.implicitConversions
 import scala.reflect.ClassTag
+import scala.reflect.runtime.universe.TypeTag
 import scala.collection.JavaConversions._
 
 import com.fasterxml.jackson.core.JsonFactory
@@ -29,7 +30,7 @@ import org.apache.spark.api.java.JavaRDD
 import org.apache.spark.api.python.SerDeUtil
 import org.apache.spark.rdd.RDD
 import org.apache.spark.storage.StorageLevel
-import org.apache.spark.sql.catalyst.{SqlParser, ScalaReflection}
+import org.apache.spark.sql.catalyst.{expressions, SqlParser, ScalaReflection}
 import org.apache.spark.sql.catalyst.analysis.{ResolvedStar, UnresolvedRelation}
 import org.apache.spark.sql.catalyst.expressions._
 import org.apache.spark.sql.catalyst.plans.{JoinType, Inner}
@@ -39,7 +40,6 @@ import org.apache.spark.sql.json.JsonRDD
 import org.apache.spark.sql.sources._
 import org.apache.spark.sql.types.{NumericType, StructType}
 
-
 /**
  * Internal implementation of [[DataFrame]]. Users of the API should use [[DataFrame]] directly.
  */
@@ -292,6 +292,18 @@ private[sql] class DataFrameImpl protected[sql](
     Sample(fraction, withReplacement, seed, logicalPlan)
   }
 
+  override def explode[A <: Product : TypeTag]
+      (input: Column*)(f: Row => TraversableOnce[A]): DataFrame = {
+    val schema = ScalaReflection.schemaFor[A].dataType.asInstanceOf[StructType]
+    val attributes = schema.toAttributes
+    val rowFunction =
+      f.andThen(_.map(ScalaReflection.convertToCatalyst(_, schema).asInstanceOf[Row]))
+    val generator = UserDefinedGenerator(attributes, rowFunction, input.map(_.expr))
+
+    Generate(generator, join = true, outer = false, None, logicalPlan)
+  }
+
+
   /////////////////////////////////////////////////////////////////////////////
   // RDD API
   /////////////////////////////////////////////////////////////////////////////

sql/core/src/main/scala/org/apache/spark/sql/IncomputableColumn.scala

@@ -18,6 +18,7 @@
 package org.apache.spark.sql
 
 import scala.reflect.ClassTag
+import scala.reflect.runtime.universe.TypeTag
 
 import org.apache.spark.api.java.JavaRDD
 import org.apache.spark.rdd.RDD
@@ -114,7 +115,10 @@ private[sql] class IncomputableColumn(protected[sql] val expr: Expression) exten
 
   override def sample(withReplacement: Boolean, fraction: Double, seed: Long): DataFrame = err()
 
-  /////////////////////////////////////////////////////////////////////////////
+  override def explode[A <: Product : TypeTag]
+      (input: Column*)(f: Row => TraversableOnce[A]): DataFrame = err()
+
+    /////////////////////////////////////////////////////////////////////////////
 
   override def head(n: Int): Array[Row] = err()
 

sql/core/src/test/scala/org/apache/spark/sql/DataFrameSuite.scala

@@ -98,6 +98,22 @@ class DataFrameSuite extends QueryTest {
       sql("SELECT a.key, b.key FROM testData a JOIN testData b ON a.key = b.key").collect().toSeq)
   }
 
+  test("explode") {
+    val df = Seq((1, "a b c"), (2, "a b"), (3, "a")).toDataFrame("number", "letters")
+    val df2 =
+      df.explode('letters) {
+        case Row(letters: String) => letters.split(" ").map(Tuple1(_)).toSeq
+      }
+
+    checkAnswer(
+      df2
+        .select('_1 as 'letter, 'number)
+        .groupBy('letter)
+        .agg('letter, countDistinct('number)),
+      Row("a", 3) :: Row("b", 2) :: Row("c", 1) :: Nil
+    )
+  }
+
   test("selectExpr") {
     checkAnswer(
       testData.selectExpr("abs(key)", "value"),