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Summing previous rows over a grouping

    Question

  • For a given grouping, I want to sum values in a column from previous rows and subtract the value in the same column for the current row. This was initially coded as a custom Processor, but I can't find a way to sort and group the values. I see PRESORT exists for Reducer, but I haven't found a way to use it in a Processor as I keep getting compile-time errors.

    Another option is to use OVER() with a custom Aggregator, but I haven't found any documentation on how to do that.

    Thoughts on how best to do this or further documentation?

    Wednesday, August 3, 2016 4:53 PM

Answers

  • PRESORT only exists for reducers. Why can't you try using a reducer (that aggregates the values but does produce one output row per input)?

    Custom aggregators are currently not supported with the OVER expression. Please file a request at http://aka.ms/adlfeedback.


    Michael Rys

    Monday, August 8, 2016 7:40 PM
    Moderator

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