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From Michele Bertoni <michele1.bert...@mail.polimi.it>
Subject Re: sorting groups
Date Wed, 17 Jun 2015 06:35:31 GMT
Hi Fabian,
My dataset is of this type
RegionType (Long, String, Long, Long, Char, Array[GValue])
Where GValue is a case class implemented by
GString(v:String)
GDouble(v:Double)

I have two case of sorting:
In the first (topk) i have to group by the first field of the regions and sort by a set of
fields of the GValue array

In the second (topg) i have to sort by the first field of the regions and by a set of fields
of the array, then sort by one field of the array

For grouping i am using the groupby function with a function as parameter that creates the
hash of the desired fields, something like
ds.groupby((r:RegionType) =>
  s = new stringBuilder
  s.append(r._1)
  grouping.init.foreach((index:int) =>
    s.append("#")
    s.append(r._6(index))
  )
  Md5.hash(s.toString)
)

Then i sort it using (in the topg case, the second)
.sortGroup(((r:RegionType)=>
  r._6(grouping.last ) /*here i am doing some cast, i am writing from my smartphone i don't
remember all the details sorry*/ ),Order.ASCENDING)

in the first case instead i group only by r._1 and i have a recursive function that appends
sortgroup operator to the grouoed dataset

Is there a way to solve this?

I think i don't understand what a keySelector is


Thanks!
Michele
________________________________
Da: Fabian Hueske <fhueske@gmail.com>
Inviato: martedì 16 giugno 2015 23.43.03
A: user@flink.apache.org
Oggetto: Re: sorting groups

Hi,

the error is related to the way you specify the grouping and the sorting key.
The API is currently restricted in the way, that you can only use a key selector function
for the sorting key if you also used a selector function for the grouping key.

In Scala the use of key selector functions is often not very obvious.

If you post the groupBy().sortGroup() command and the input type, I can help you getting it
right.

Cheers, Fabian

2015-06-16 23:37 GMT+02:00 Michele Bertoni <michele1.bertoni@mail.polimi.it<mailto:michele1.bertoni@mail.polimi.it>>:
Hi everybody,
I am trying to sorting a grouped dataset, but i am getting this error:

Exception in thread "main" org.apache.flink.api.common.InvalidProgramException: Sorting on
KeySelector keys only works with KeySelector grouping.
        at org.apache.flink.api.scala.GroupedDataSet.sortGroup(GroupedDataSet.scala:113)
        at it.polimi.genomics.flink.FlinkImplementation.regionOperation.OrderRD$.sort(OrderRD.scala:82)
        ...

can anybody help me understanding the error?
i have no idea what it means and google is not helpful in this case


thanks!
cheers
Michele


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