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From John Peterson <>
Subject [Java] Map as key or value in Map (nested maps)
Date Sat, 02 Jan 2021 06:02:10 GMT
Hi All,

I’m attempting to convert the following data structure into vectors for

Map<String, Map<String, Integer>>

Using the UnionMapWriter, it seems that I can’t grab a map writer for the
value of the map, but a nested complex type such as a list is supported:

writer.value().list(); // works, get a ListWriter
writer.value().map(); // doesn’t work, no such method

Is this a known limitation, or is there a proper way to translate nested
map structures to Arrow? I’m planning on supporting a Map as both a key and
a value of a map. If there is a way to do this (even without the writers),
could you please point me to an example?

Thanks in advance for your help with this.


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