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https://issues.apache.org/jira/browse/SPARK-8999?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Xiangrui Meng updated SPARK-8999:
---------------------------------
    Description: 
In SPARK-6487, we assume that all items are ordered. However, we should support 
non-temporal sequences in PrefixSpan. This should be done before 1.5 because it 
changes PrefixSpan APIs.

We can use `Array[Array[Int]]` or follow SPMF to use `Array[Int]` and use -1 to 
mark itemset boundaries. The latter is more efficient for storage. If we 
support generic item type, we can use null.

  was:
In SPARK-6487, we assume that all items are ordered. However, we should support 
non-temporal sequences in PrefixSpan. This should be done before 1.5 because it 
changes PrefixSpan APIs.

We can use `Array[Array[Int]]` or follow SPMF to use `Array[Int]` and use -1 to 
mark itemset boundaries. If we support generic item type, we can use null.


> Support non-temporal sequence in PrefixSpan
> -------------------------------------------
>
>                 Key: SPARK-8999
>                 URL: https://issues.apache.org/jira/browse/SPARK-8999
>             Project: Spark
>          Issue Type: Improvement
>          Components: MLlib
>    Affects Versions: 1.5.0
>            Reporter: Xiangrui Meng
>            Priority: Critical
>
> In SPARK-6487, we assume that all items are ordered. However, we should 
> support non-temporal sequences in PrefixSpan. This should be done before 1.5 
> because it changes PrefixSpan APIs.
> We can use `Array[Array[Int]]` or follow SPMF to use `Array[Int]` and use -1 
> to mark itemset boundaries. The latter is more efficient for storage. If we 
> support generic item type, we can use null.



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