Terms Component

The Terms Component provides access to the indexed terms in a field and the number of documents that match each term. This can be useful for building an auto-suggest feature or any other feature that operates at the term level instead of the search or document level. Retrieving terms in index order is very fast since the implementation directly uses Lucene’s TermEnum to iterate over the term dictionary.

In a sense, this search component provides fast field-faceting over the whole index, not restricted by the base query or any filters. The document frequencies returned are the number of documents that match the term, including any documents that have been marked for deletion but not yet removed from the index.

Configuring the Terms Component

Terms Component is one of the default search components and does not need to be defined in solrconfig.xml.

The definition is equivalent to:

<searchComponent name="terms" class="solr.TermsComponent"/>

Using the Terms Component in a Request Handler

Solr comes with an implicit request handler definition /terms, which enables (only) Terms component.

If you want to enable Terms component when using another Request Handler, terms=true parameter needs to be passed during the request or be set in the handler’s defaults.

Terms Component Parameters

The parameters below allow you to control what terms are returned. You can also configure any of these with the request handler if you’d like to set them permanently. Or, you can add them to the query request. These parameters are:

terms

Optional

Default: false

If set to true, enables the Terms Component.

Example: terms=true

terms.fl

Required

Default: none

Specifies the field from which to retrieve terms. This parameter is required if terms=true. This parameter can be specified multiple times to retrieve terms for different fields.

Example: terms.fl=title

Example: terms.fl=title&terms=true&terms.fl=name&terms.list=cable,sony

<response>
   <lst name="responseHeader">
      <bool name="zkConnected">true</bool>
      <int name="status">0</int>
      <int name="QTime">4</int>
   </lst>
   <lst name="terms">
      <lst name="name">
         <int name="cable">8661</int>
         <int name="sony">21</int>
      </lst>
      <lst name="title">
         <int name="cable">11387</int>
         <int name="sony">3921</int>
      </lst>
   </lst>
</response>

terms.list

Optional

Default: none

Fetches the document frequency for a comma-delimited list of terms. Terms are always returned in index order. If terms.ttf is set to true, also returns their total term frequency. If multiple terms.fl are defined, these statistics will be returned for each term in each requested field.

Example: terms.list=termA,termB,termC

When terms.list is specified, then terms are always sorted by index. Except terms.ttf, none of other terms parameters are supported when terms.list is specified.

terms.limit

Optional

Default: 10

Specifies the maximum number of terms to return. If the limit is set to a number less than 0, then no maximum limit is enforced. Although this is not required, either this parameter or terms.upper must be defined.

Example: terms.limit=20

terms.lower

Optional

Default: see description

Specifies the term at which to start. If not specified, the empty string is used, causing Solr to start at the beginning of the field.

Example: terms.lower=orange

terms.lower.incl

Optional

Default: true

If set to true, includes the lower-bound term (specified with terms.lower in the result set.

Example: terms.lower.incl=false

terms.mincount

Optional

Default: 1

Specifies the minimum document frequency to return in order for a term to be included in a query response. Results are inclusive of the mincount (that is, >= mincount).

Example: terms.mincount=5

terms.maxcount

Optional

Default: -1

Specifies the maximum document frequency a term must have in order to be included in a query response. The default setting is -1, which sets no upper bound. Results are inclusive of the maxcount (that is, <= maxcount).

Example: terms.maxcount=25

terms.prefix

Optional

Default: none

Restricts matches to terms that begin with the specified string.

Example: terms.prefix=inter

terms.raw

Optional

Default: false

If set to true, returns the raw characters of the indexed term, regardless of whether it is human-readable. For instance, the indexed form of numeric numbers is not human-readable.

Example: terms.raw=true

terms.regex

Optional

Default: none

Restricts matches to terms that match the regular expression.

Example: terms.regex=.*pedist

terms.regex.flag

Optional

Default: none

Defines a Java regex flag to use when evaluating the regular expression defined with terms.regex. See http://docs.oracle.com/javase/tutorial/essential/regex/pattern.html for details of each flag. Valid options are:

case_insensitive
comments
multiline
literal
dotall
unicode_case
canon_eq
unix_lines

Example: terms.regex.flag=case_insensitive

terms.stats

Optional

Default: false

If true, include index statistics in the results. Currently returns only the number of documents for a collection. When combined with terms.list it provides enough information to compute inverse document frequency (IDF) for a list of terms.

terms.sort

Optional

Default: count

Defines how to sort the terms returned. Valid options are count, which sorts by the term frequency, with the highest term frequency first, or index, which sorts in index order.

Example: terms.sort=index

terms.ttf

Optional

Default: false

If set to true, returns both df (docFreq) and ttf (totalTermFreq) statistics for each requested term in terms.list. In this case, the response format is:

XML:

<lst name="terms">
  <lst name="field">
    <lst name="termA">
      <long name="df">22</long>
      <long name="ttf">73</long>
    </lst>
  </lst>
</lst>

JSON:

{
  "terms": {
    "field": [
      "termA",
      {
        "df": 22,
        "ttf": 73
      }
    ]
  }
}

terms.upper

Optional

Default: none

Specifies the term to stop at. Although this parameter is not required, either this parameter or terms.limit must be defined.

Example: terms.upper=plum

terms.upper.incl

Optional

Default: false

If set to true, the upper bound term is included in the result set.

Example: terms.upper.incl=true

The response to a terms request is a list of the terms and their document frequency values.

You may also be interested in the TermsComponent javadoc.

Terms Component Examples

All of the following sample queries work with Solr’s “bin/solr start -e techproducts” example.

Get Top 10 Terms

This query requests the first ten terms in the name field:

http://localhost:8983/solr/techproducts/terms?terms.fl=name&wt=xml

Results:

<response>
  <lst name="responseHeader">
    <int name="status">0</int>
    <int name="QTime">2</int>
  </lst>
  <lst name="terms">
    <lst name="name">
      <int name="one">5</int>
      <int name="184">3</int>
      <int name="1gb">3</int>
      <int name="3200">3</int>
      <int name="400">3</int>
      <int name="ddr">3</int>
      <int name="gb">3</int>
      <int name="ipod">3</int>
      <int name="memory">3</int>
      <int name="pc">3</int>
    </lst>
  </lst>
</response>

Get First 10 Terms Starting with Letter 'a'

This query requests the first ten terms in the name field, in index order (instead of the top 10 results by document count):

http://localhost:8983/solr/techproducts/terms?terms.fl=name&terms.lower=a&terms.sort=index&wt=xml

Results:

<response>
  <lst name="responseHeader">
    <int name="status">0</int>
    <int name="QTime">0</int>
  </lst>
  <lst name="terms">
    <lst name="name">
      <int name="a">1</int>
      <int name="all">1</int>
      <int name="apple">1</int>
      <int name="asus">1</int>
      <int name="ata">1</int>
      <int name="ati">1</int>
      <int name="belkin">1</int>
      <int name="black">1</int>
      <int name="british">1</int>
      <int name="cable">1</int>
    </lst>
  </lst>
</response>

Using Terms Component in a Request Handler

This query augments a regular search with terms information.

http://localhost:8983/solr/techproducts/select?q=corsair&fl=id,name&rows=1&echoParams=none&wt=xml&terms=true&terms.fl=name

Results (notice that the term counts are not affected by the query):

<response>

<lst name="responseHeader">
  <int name="status">0</int>
  <int name="QTime">1</int>
</lst>
<result name="response" numFound="2" start="0" numFoundExact="true">
  <doc>
    <str name="id">VS1GB400C3</str>
    <str name="name">CORSAIR ValueSelect 1GB 184-Pin DDR SDRAM Unbuffered DDR 400 (PC 3200) System Memory - Retail</str></doc>
</result>
<lst name="terms">
  <lst name="name">
    <int name="one">5</int>
    <int name="184">3</int>
    <int name="1gb">3</int>
    <int name="3200">3</int>
    <int name="400">3</int>
    <int name="ddr">3</int>
    <int name="gb">3</int>
    <int name="ipod">3</int>
    <int name="memory">3</int>
    <int name="pc">3</int>
  </lst>
</lst>
</response>

SolrJ Invocation

    SolrQuery query = new SolrQuery();
    query.setRequestHandler("/terms");
    query.setTerms(true);
    query.setTermsLimit(5);
    query.setTermsLower("s");
    query.setTermsPrefix("s");
    query.addTermsField("terms_s");
    query.setTermsMinCount(1);

    QueryRequest request = new QueryRequest(query);
    List<Term> terms = request.process(getSolrClient()).getTermsResponse().getTerms("terms_s");

Using the Terms Component for an Auto-Suggest Feature

If the Suggester doesn’t suit your needs, you can use the Terms component in Solr to build a similar feature for your own search application. Simply submit a query specifying whatever characters the user has typed so far as a prefix. For example, if the user has typed "at", the search engine’s interface would submit the following query:

http://localhost:8983/solr/techproducts/terms?terms.fl=name&terms.prefix=at&wt=xml

Result:

<response>
  <lst name="responseHeader">
    <int name="status">0</int>
    <int name="QTime">1</int>
  </lst>
  <lst name="terms">
    <lst name="name">
      <int name="ata">1</int>
      <int name="ati">1</int>
    </lst>
  </lst>
</response>

You can use the parameter omitHeader=true to omit the response header from the query response, like in this example, which also returns the response in JSON format:

http://localhost:8983/solr/techproducts/terms?terms.fl=name&terms.prefix=at&omitHeader=true

Result:

{
  "terms": {
    "name": [
      "ata",
      1,
      "ati",
      1
    ]
  }
}