[SPARK-5639][SQL] Support DataFrame.renameColumn.

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

@@ -36,7 +36,8 @@ private[sql] object DataFrame {
 
 
 /**
- * A collection of rows that have the same columns.
+ * :: Experimental ::
+ * A distributed collection of data organized into named columns.
  *
  * A [[DataFrame]] is equivalent to a relational table in Spark SQL, and can be created using
  * various functions in [[SQLContext]].
@@ -72,6 +73,7 @@ private[sql] object DataFrame {
  * }}}
  */
 // TODO: Improve documentation.
+@Experimental
 trait DataFrame extends RDDApi[Row] {
 
   val sqlContext: SQLContext
@@ -425,6 +427,11 @@ trait DataFrame extends RDDApi[Row] {
    */
   def addColumn(colName: String, col: Column): DataFrame
 
+  /**
+   * Returns a new [[DataFrame]] with a column renamed.
+   */
+  def renameColumn(existingName: String, newName: String): DataFrame
+
   /**
    * Returns the first `n` rows.
    */

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

@@ -238,6 +238,14 @@ private[sql] class DataFrameImpl protected[sql](
     select(Column("*"), col.as(colName))
   }
 
+  override def renameColumn(existingName: String, newName: String): DataFrame = {
+    val colNames = schema.map { field =>
+      val name = field.name
+      if (name == existingName) Column(name).as(newName) else Column(name)
+    }
+    select(colNames :_*)
+  }
+
   override def head(n: Int): Array[Row] = limit(n).collect()
 
   override def head(): Row = head(1).head

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

@@ -108,6 +108,8 @@ private[sql] class IncomputableColumn(protected[sql] val expr: Expression) exten
 
   override def addColumn(colName: String, col: Column): DataFrame = err()
 
+  override def renameColumn(existingName: String, newName: String): DataFrame = err()
+
   override def head(n: Int): Array[Row] = err()
 
   override def head(): Row = err()

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

@@ -313,6 +313,27 @@ class DataFrameSuite extends QueryTest {
     )
   }
 
+  test("addColumn") {
+    val df = testData.toDataFrame.addColumn("newCol", col("key") + 1)
+    checkAnswer(
+      df,
+      testData.collect().map { case Row(key: Int, value: String) =>
+        Row(key, value, key + 1)
+      }.toSeq)
+    assert(df.schema.map(_.name).toSeq === Seq("key", "value", "newCol"))
+  }
+
+  test("renameColumn") {
+    val df = testData.toDataFrame.addColumn("newCol", col("key") + 1)
+      .renameColumn("value", "valueRenamed")
+    checkAnswer(
+      df,
+      testData.collect().map { case Row(key: Int, value: String) =>
+        Row(key, value, key + 1)
+      }.toSeq)
+    assert(df.schema.map(_.name).toSeq === Seq("key", "valueRenamed", "newCol"))
+  }
+
   test("apply on query results (SPARK-5462)") {
     val df = testData.sqlContext.sql("select key from testData")
     checkAnswer(df("key"), testData.select('key).collect().toSeq)