It fails to sort a grouped data frame

[holgerbrandl]

When running

irisData.groupBy("Species").sortBy("Sepal.Length")

it fails with

java.lang.IllegalStateException: Can not use ColumnGroup as sort column

However, sorting by group is a common usecase. In particular in combination with next() and prev()

[koperagen]

Thank you for the report! It looks like a bug, because this seems to be working fine:

irisData.groupBy("Species")
        .sortBy { it["Petal.Length"] }

In particular in combination with next() and prev()

Can you elaborate?

[holgerbrandl]

I'm happy to help but I'm unsure about what you would need. It seems, you can reproduce the problem already?

[koperagen]

Yes, i can reproduce the problem. I don't understand how and when one could use next() and prev() in sorting though. So i'm curious about the use case and maybe an example?

[holgerbrandl]

One use case that comes to mind are tool-state changes (ie. in manufacturing). Tools periodically change their status (idle, productive, maintenance, etc.). Later one, one may want to compute the duration for which each tool is in a specific state. To do s, we need to

toolEvents.groupBy("tool_id").sortedBy("timestamp").add("state_duration"){ last timestamp - current).aggregate ... plot...

Unfortunately I do not have shareable example data at the moment.

[koperagen]

I really like this example, thank you.

[Jolanrensen]

fixed and merged!