arrow-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Micah Kornfield <>
Subject Re: [Java] Map as key or value in Map (nested maps)
Date Mon, 04 Jan 2021 19:41:35 GMT
Hi John,
I believe this is an oversight in the API.  I think we should probably open
up a JIRA and try to address it.

Depending on the use-case you might be able to write a map as
list-of-struct<key, value> and replace the metadata at some point, but I'm
not sure if this is possible in the Java library, so I don't have any


On Fri, Jan 1, 2021 at 10:02 PM John Peterson <>

> Hi All,
> I’m attempting to convert the following data structure into vectors for
> Arrow:
> 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.
> John

View raw message