[SPARK-6635][SQL] DataFrame.withColumn should replace columns with id…

…entical column names

JIRA https://issues.apache.org/jira/browse/SPARK-6635

Author: Liang-Chi Hsieh <viirya@gmail.com>

Closes apache#5541 from viirya/replace_with_column and squashes the following commits:

b539c7b [Liang-Chi Hsieh] For comment.
72f35b1 [Liang-Chi Hsieh] DataFrame.withColumn can replace original column with identical column name.

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

@@ -747,7 +747,19 @@ class DataFrame private[sql](
    * Returns a new [[DataFrame]] by adding a column.
    * @group dfops
    */
-  def withColumn(colName: String, col: Column): DataFrame = select(Column("*"), col.as(colName))
+  def withColumn(colName: String, col: Column): DataFrame = {
+    val resolver = sqlContext.analyzer.resolver
+    val replaced = schema.exists(f => resolver(f.name, colName))
+    if (replaced) {
+      val colNames = schema.map { field =>
+        val name = field.name
+        if (resolver(name, colName)) col.as(colName) else Column(name)
+      }
+      select(colNames :_*)
+    } else {
+      select(Column("*"), col.as(colName))
+    }
+  }
 
   /**
    * Returns a new [[DataFrame]] with a column renamed.

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

@@ -473,6 +473,14 @@ class DataFrameSuite extends QueryTest {
     assert(df.schema.map(_.name).toSeq === Seq("key", "value", "newCol"))
   }
 
+  test("replace column using withColumn") {
+    val df2 = TestSQLContext.sparkContext.parallelize(Array(1, 2, 3)).toDF("x")
+    val df3 = df2.withColumn("x", df2("x") + 1)
+    checkAnswer(
+      df3.select("x"),
+      Row(2) :: Row(3) :: Row(4) :: Nil)
+  }
+
   test("withColumnRenamed") {
     val df = testData.toDF().withColumn("newCol", col("key") + 1)
       .withColumnRenamed("value", "valueRenamed")