[GitHub] [arrow-datafusion] jorgecarleitao commented on issue #600: Allow User Defined Aggregates to return multiple values / structs

[GitBox <gi...@apache.org>]

jorgecarleitao commented on issue #600:
URL: https://github.com/apache/arrow-datafusion/issues/600#issuecomment-866233559


   When I implemented todays' aggs, I Initially though about multiple return values, and then concluded that the Struct is sufficient and desirable. What I like about the struct is that it enables named fields, which imo makes the statements rather expressive. E.g. 
   
   ```
   df = df.agg(udaf.call("a").alias("a"))
   df.select(df["a"]["min"], df["a"]["max"])
   ```
   
   vs 
   
   ```
   df = df.agg(udaf.call("a").alias("a"))
   df.select(df["a"][0], df["a"][1])
   ```
   
   the context "min" and "max" imo helps the user at reading what they are extracting from the column.
   
   Would supporting structs for ScalarValues solve this nicely?


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