Filtering and faceting multivalue fields in SOLR

Question

I using SOLR 4 and have a document schema that contains a multivalued field. The schema looks something like this:

... some fields
"foo": [
    "aaa",
    "abb",
    "baa",
    "bbb"
],
... more fields

I would like to get the count of all documents with each value of the "foo" variable:

• aaa was in the foo list of 45 documents
• abb was in the foo list of 76 documents
• baa was in the foo list of 44 documents
• bbb was in the foo list of 52 documents

To make things slightly more complicated, I would like to filter which facets are returned (in the above example, let's say only the ones beginning with "a"):

• aaa was in the foo list of 23 documents
• abb was in the foo list of 76 documents

I think I need to filter the facets somehow but I'm at a loss how to begin. Suggestions welcome!

Answer 1

I think field collapsing might be helpful:

https://cwiki.apache.org/confluence/display/solr/Result+Grouping

Answer 2

The facet.prefix parameter limits the terms on which to facet to those starting with the given string prefix.

q=*
&facet=true
&facet.field=foo
&facet.prefix=a

Above query will filter the facets and return you only those which starts with a.