[LUCENE-3097] Post grouping faceting

• Type: New Feature
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Fix Version/s: 3.4, 4.0-ALPHA
• Component/s: modules/grouping
• Lucene Fields: Patch Available
• Assignee: Martijn van Groningen
• Reporter: Martijn van Groningen
• Created: 14/May/11 14:10
• Updated: 28/Aug/22 12:46
• Resolved: 14/Nov/11 12:22

Description

This issues focuses on implementing post grouping faceting.

• How to handle multivalued fields. What field value to show with the facet.
• Where the facet counts should be based on
  • Facet counts can be based on the normal documents. Ungrouped counts.
  • Facet counts can be based on the groups. Grouped counts.
  • Facet counts can be based on the combination of group value and facet value. Matrix counts.

And properly more implementation options.

The first two methods are implemented in the SOLR-236 patch. For the first option it calculates a DocSet based on the individual documents from the query result. For the second option it calculates a DocSet for all the most relevant documents of a group. Once the DocSet is computed the FacetComponent and StatsComponent use one the DocSet to create facets and statistics.

This last one is a bit more complex. I think it is best explained with an example. Lets say we search on travel offers:

hotel	departure_airport	duration
Hotel a	AMS	5
Hotel a	DUS	10
Hotel b	AMS	5
Hotel b	AMS	10

If we group by hotel and have a facet for airport. Most end users expect (according to my experience off course) the following airport facet:
AMS: 2
DUS: 1

The above result can't be achieved by the first two methods. You either get counts AMS:3 and DUS:1 or 1 for both airports.

Issue Links

• is blocked by: LUCENE-3079 Faceting module
• is depended upon by: SOLR-2665 Solr Post Group Faceting
• relates to: LUCENE-1421 Ability to group search results by field