[GitHub] [incubator-druid] AlexanderSaydakov commented on issue #7486: regression: quantilesDoublesSketch returns null instead of empty array

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AlexanderSaydakov commented on issue #7486: regression: quantilesDoublesSketch returns null instead of empty array 
URL: https://github.com/apache/incubator-druid/issues/7486#issuecomment-484987840
 
 
   Let's see:
   Druid 0.14 uses sketches-core-0.12.0
   Druid 0.13 uses sketches-core-0.10.3
   This behavior changed in sketches-core-0.11.0
   I believe that previous behavior was to always return an array of quantile values corresponding to the specified ranks. In case of an empty sketch the values returned are NaN, not an empty array. We thought that array of NaN values does not make much sense, so we changed this to return null. This affects all functions returning arrays: getQuantiles(), getPMF() and getCDF()
   
   If null result is undesirable in Druid, it should be changed in the post-aggs.
   Could you clarify why null result from an empty sketch is not desirable? Why an array of NaNs was better?

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