Hello,
I'd like some clarification on the spec and intent for dense arrays. Currently, it is specified that offsets of a dense union are "in order / increasing" (*). However, it is not obvious whether repeated values are allowed or not. I suspect the intent is to avoid having people exploit unions as some kind of poor man's dictionaries. Also, perhaps some optimizations are possible if monotonic or strictly monotonic indices are assumed? But I don't know the history behind the union type. Regards Antoine. (*) https://arrow.apache.org/docs/format/Columnar.html#dense-union
