Unique() metrics not supported in Solr Streaming facet stream source

[Zheng Lin Edwin Yeo]

Hi,

We are working on the Solr Streaming expression, using the facet stream
source.

As the underlying structure is using JSON Facet, would like to find out why
the unique() metrics is not supported? Currently, it only supports sum(col)
, avg(col), min(col), max(col), count(*)

I'm using Solr 6.5.1

Regards,
Edwin