[SPARK-11889][SQL] Fix type inference for GroupedDataset.agg in REPL

In this PR I delete a method that breaks type inference for aggregators (only in the REPL)

The error when this method is present is:
```
<console>:38: error: missing parameter type for expanded function ((x$2) => x$2._2)
              ds.groupBy(_._1).agg(sum(_._2), sum(_._3)).collect()
```

Author: Michael Armbrust <michael@databricks.com>

Closes #9870 from marmbrus/dataset-repl-agg.

1 files changed, 24 insertions, 0 deletions

diff --git a/repl/scala-2.10/src/test/scala/org/apache/spark/repl/ReplSuite.scala b/repl/scala-2.10/src/test/scala/org/apache/spark/repl/ReplSuite.scala
index 081aa03002..cbcccb11f1 100644
--- a/repl/scala-2.10/src/test/scala/org/apache/spark/repl/ReplSuite.scala
+++ b/repl/scala-2.10/src/test/scala/org/apache/spark/repl/ReplSuite.scala
@@ -339,6 +339,30 @@ class ReplSuite extends SparkFunSuite {
     }
   }
 
+  test("Datasets agg type-inference") {
+    val output = runInterpreter("local",
+      """
+        |import org.apache.spark.sql.functions._
+        |import org.apache.spark.sql.Encoder
+        |import org.apache.spark.sql.expressions.Aggregator
+        |import org.apache.spark.sql.TypedColumn
+        |/** An `Aggregator` that adds up any numeric type returned by the given function. */
+        |class SumOf[I, N : Numeric](f: I => N) extends Aggregator[I, N, N] with Serializable {
+        |  val numeric = implicitly[Numeric[N]]
+        |  override def zero: N = numeric.zero
+        |  override def reduce(b: N, a: I): N = numeric.plus(b, f(a))
+        |  override def merge(b1: N,b2: N): N = numeric.plus(b1, b2)
+        |  override def finish(reduction: N): N = reduction
+        |}
+        |
+        |def sum[I, N : Numeric : Encoder](f: I => N): TypedColumn[I, N] = new SumOf(f).toColumn
+        |val ds = Seq((1, 1, 2L), (1, 2, 3L), (1, 3, 4L), (2, 1, 5L)).toDS()
+        |ds.groupBy(_._1).agg(sum(_._2), sum(_._3)).collect()
+      """.stripMargin)
+    assertDoesNotContain("error:", output)
+    assertDoesNotContain("Exception", output)
+  }
+
   test("collecting objects of class defined in repl") {
     val output = runInterpreter("local[2]",
       """