DataFrame.withColumn can replace original column with identical column name.

Author: viirya

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

@@ -457,6 +457,10 @@ class DataFrameSuite extends QueryTest {
         Row(key, value, key + 1)
       }.toSeq)
     assert(df.schema.map(_.name).toSeq === Seq("key", "value", "newCol"))
+
+    val df2 = TestSQLContext.sparkContext.parallelize(Array(1, 2, 3)).toDF("x")
+    val df3 = df2.withColumn("x", df2("x") + 1)
+    assert(df3.select("x").collect().toSeq === Seq(Row(2), Row(3), Row(4)))
   }
 
   test("withColumnRenamed") {