Tim Owen created SOLR-11765:
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Summary: Ability to Facet on a Function
Key: SOLR-11765
URL: https://issues.apache.org/jira/browse/SOLR-11765
Project: Solr
Issue Type: Improvement
Security Level: Public (Default Security Level. Issues are Public)
Components: Facet Module, JSON Request API
Reporter: Tim Owen
This is an extension to the JSON facet functionality, to support faceting on a
function. I have extended the parsing of json.facet to allow a 4th facet type
(function) and you provide a function expression. You can also provide sort,
limit and mincount, as it behaves similarly to faceting on a field. Subfacets
work as normal - you can nest function facets anywhere you can use other types.
The output is in the same format as field facets, but with a bucket per
distinct value produced by the function. Hence the usage of this is most
appropriate for situations where your function only produces a relatively small
number of possible values. It's also recommended to have docValues on any field
used by the function.
Our initial use-case for this is with a function that extracts a given part
from a date field's value e.g. day of week, or hour of day, where the possible
range of output values is very low.
Still TODO: documentation, unit tests, and possible extensions to support a
missing bucket and functional sorting (currently it's only sortable by the
bucket label or by volume)
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