Wes McKinney created ARROW-3144:
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Summary: [C++] Better solution for cases where dictionaries are
unknown at schema reconstruction time, or for delta dictionaries
Key: ARROW-3144
URL: https://issues.apache.org/jira/browse/ARROW-3144
Project: Apache Arrow
Issue Type: Improvement
Components: C++
Reporter: Wes McKinney
Fix For: 0.12.0
There are a couple of inter-related issues:
* Cases where a system might send the schema without the dictionaries, and the
user wishes to reason about the schema and its types without knowing the
dictionary values
* Dictionaries that are changing, e.g. using delta dictionary messages
{{arrow::DictionaryType}} has no "linkage" to any external object. I propose
adding a "LinkedDictionaryType" or something similar (purely a C++ construct),
which functionally would be a subclass of {{DictionaryType}}, which would allow
a type to be created which will obtain its dictionary later through some kind
of "Dictionary provider" interface. There is something similar in Java already.
This would allow a dictionary to evolve via delta dictionaries, or for a
dictionary to be retrieved later e.g. through an RPC or IPC layer
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