Github user srowen commented on a diff in the pull request:
https://github.com/apache/spark/pull/20578#discussion_r167439487
--- Diff: mllib/src/main/scala/org/apache/spark/ml/fpm/FPGrowth.scala ---
@@ -158,18 +159,30 @@ class FPGrowth @Since("2.2.0") (
}
private def genericFit[T: ClassTag](dataset: Dataset[_]): FPGrowthModel
= {
+ val handlePersistence = dataset.storageLevel == StorageLevel.NONE
+
val data = dataset.select($(itemsCol))
- val items = data.where(col($(itemsCol)).isNotNull).rdd.map(r =>
r.getSeq[T](0).toArray)
+ val items = data.where(col($(itemsCol)).isNotNull).rdd.map(r =>
r.getSeq[Any](0).toArray)
--- End diff --
Hm, I wonder how it worked before then? maybe it is related to the caching.
But then this changes the type of `items`, and therefore `parentModel`.
Maybe it doesn't matter, just surprising.
T is a ClassTag here and `.toArray` wouldn't work otherwise. Small similar
example:
```
scala> def foo[T:scala.reflect.ClassTag](s: Seq[T]) = s.toArray
foo: [T](s: Seq[T])(implicit evidence$1: scala.reflect.ClassTag[T])Array[T]
scala> def foo[T](s: Seq[T]) = s.toArray
<console>:11: error: No ClassTag available for T
def foo[T](s: Seq[T]) = s.toArray
^
scala> def foo[T:scala.reflect.ClassTag](s: Seq[T]) = s.toArray
foo: [T](s: Seq[T])(implicit evidence$1: scala.reflect.ClassTag[T])Array[T]
scala> foo(Seq("foo", "bar"))
res3: Array[String] = Array(foo, bar)
```
oh well if it works with this change and not without, seems OK, just an
interesting curiosity.
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