Github user dragos commented on a diff in the pull request:
https://github.com/apache/spark/pull/9870#discussion_r45545095
--- Diff:
repl/scala-2.10/src/test/scala/org/apache/spark/repl/ReplSuite.scala ---
@@ -315,6 +315,30 @@ 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()
--- End diff --
I can't reproduce the difference. It won't infer it in a standalone program
[either](https://gist.github.com/dragos/7c2d3ec962ee2e6862f3).
As I mentioned in our conversation, it's a chicken and egg problem: type
inference is guided by the expected type, but if the method is overloaded, the
expected type is not known. And the argument type is what guides overload
resolution. It works in simple cases, when the overloads have different
aritites, but with varargs that's no longer the case.
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