Re: sorting groups

[Michele Bertoni]

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 <fhue...@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.bert...@mail.polimi.it<mailto:michele1.bert...@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