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https://issues.apache.org/jira/browse/SPARK-18230?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15633917#comment-15633917
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Sean Owen commented on SPARK-18230:
-----------------------------------
Agree, I can't see how you'd return anything in this case. A Rating with value
NaN doesn't make sense. (Why just one?)
In fact, returning no recommendations is a valid response for an existing user,
so the response for a non-existent user could, and probably should, be
different. I think it's OK to view it as exceptional.
> MatrixFactorizationModel.recommendProducts throws NoSuchElement exception
> when the user does not exist
> ------------------------------------------------------------------------------------------------------
>
> Key: SPARK-18230
> URL: https://issues.apache.org/jira/browse/SPARK-18230
> Project: Spark
> Issue Type: Improvement
> Components: MLlib
> Affects Versions: 2.0.1
> Reporter: Mikael Ståldal
> Priority: Minor
>
> When invoking {{MatrixFactorizationModel.recommendProducts(Int, Int)}} with a
> non-existing user, a {{java.util.NoSuchElementException}} is thrown:
> {code}
> java.util.NoSuchElementException: next on empty iterator
> at scala.collection.Iterator$$anon$2.next(Iterator.scala:39)
> at scala.collection.Iterator$$anon$2.next(Iterator.scala:37)
> at
> scala.collection.IndexedSeqLike$Elements.next(IndexedSeqLike.scala:63)
> at scala.collection.IterableLike$class.head(IterableLike.scala:107)
> at
> scala.collection.mutable.WrappedArray.scala$collection$IndexedSeqOptimized$$super$head(WrappedArray.scala:35)
> at
> scala.collection.IndexedSeqOptimized$class.head(IndexedSeqOptimized.scala:126)
> at scala.collection.mutable.WrappedArray.head(WrappedArray.scala:35)
> at
> org.apache.spark.mllib.recommendation.MatrixFactorizationModel.recommendProducts(MatrixFactorizationModel.scala:169)
> {code}
> It would be nice if it returned the empty array, or throwed a more specific
> exception, and that was documented in ScalaDoc for the method.
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