How to select distinct field values using Solr?

Question

Faceting would get you a results set that contains distinct values for a field.

E.g.

http://localhost:8983/solr/select/?q=*%3A*&rows=0&facet=on&facet.field=txt

You should get something back like this:

<response>
<responseHeader><status>0</status><QTime>2</QTime></responseHeader>
<result numFound="4" start="0"/>
<lst name="facet_counts">
 <lst name="facet_queries"/>
 <lst name="facet_fields">
  <lst name="txt">
        <int name="value">100</int>
        <int name="value1">80</int>
        <int name="value2">5</int>
        <int name="value3">2</int>
        <int name="value4">1</int>
  </lst>
 </lst>
</lst>
</response>

Check out the wiki for more information. Faceting is a really cool part of solr. Enjoy :)

http://wiki.apache.org/solr/SimpleFacetParameters#Facet_Fields

Note: Faceting will show the indexed value, I.e. after all the filters have been applied. One way to get around this is to use the copyfield method, so that you can create a facet version of the txt field. THis way your results will show the original value.

Hope that helps.. Lots of documentation on faceting available on the wiki. Or I did write some with screen shots.. which you can check out here:

http://www.craftyfella.com/2010/01/faceting-and-multifaceting-syntax-in.html

For the DISTINCT part of your question, I think you may be looking for Solr's field collapsing / grouping functions. It will enable you to specify a field you want unique results from, create a group on those unique values and it will show you how many documents are that group.

You can then use the same substr stored in a separate field, and collapse on that.

Use the StatsComponent with parameter stats.calcdistinct to get a list of distinct values for a certain field:

Solr 7 https://lucene.apache.org/solr/guide/7_7/the-stats-component.html

Solr 6 https://cwiki.apache.org/confluence/display/solr/The+Stats+Component

It will also give you the count of distinct values. stats.calcdistinct is probably available since 4.7.

http://wiki.apache.org/solr/StatsComponent is outdated as it does not cover stats.calcdistinct

Example

/select?stats=on&stats.field=region&rows=0&stats.calcdistinct=true

"stats":{
  "stats_fields":{
    "region":{
      "min":"GB",
      "max":"GB",
      "count":20276,
      "missing":0,
      "distinctValues":["GB"],
      "countDistinct":1}}}}

Difference to Facets

In case of facets you need to know the count to request all, or you set the facet.limit to something really high and count the result yourself. Also, you need a string field for making facets work the way you need it here.

I would store the substring in a different field (let's call in txt_substring), then facet on txt_substring as CraftyFella showed.

Normally I'd use the n-gram tokenizer, but I don't think you can facet on that.

Solr 5.1 and later has the new Facet Module that has integrated support for finding the number of unique values in a field. You can even find the number of unique values in a field for each bucket of a facet, and sort by that value to find the highest or lowest number of unique values.

Number of unique values in "myfield": json.facet={x:'unique(myfield)'}

Facet by "category" field, and for each category, show the number of unique values in "color":

json.facet={
  cat_breakdown : { terms : {  // group results by unique values of "category"
    field : category,
    facet : {
      x : "unique(color)",  // for each category, find the number of unique colors
      y : "avg(price)"      // for each category, find the average price
    }
  }}
}

This is in Solr 5.1 and later. More facet functions like "unique" are shown at http://yonik.com/solr-facet-functions/