You're viewing version 2.19 of the OpenSearch documentation. For the latest version, see the current documentation. For information about OpenSearch version maintenance, see Release Schedule and Maintenance Policy.

Stemmer token filter

The stemmer token filter reduces words to their root or base form (also known as their stem).

Parameters

The stemmer token filter can be configured with a language parameter that accepts the following values:

• Arabic: arabic
• Armenian: armenian
• Basque: basque
• Bengali: bengali
• Brazilian Portuguese: brazilian
• Bulgarian: bulgarian
• Catalan: catalan
• Czech: czech
• Danish: danish
• Dutch: dutch, dutch_kp
• English: english (default), light_english, lovins, minimal_english, porter2, possessive_english
• Estonian: estonian
• Finnish: finnish, light_finnish
• French: light_french, french, minimal_french
• Galician: galician, minimal_galician (plural step only)
• German: light_german, german, german2, minimal_german
• Greek: greek
• Hindi: hindi
• Hungarian: hungarian, light_hungarian
• Indonesian: indonesian
• Irish: irish
• Italian: light_italian, italian
• Kurdish (Sorani): sorani
• Latvian: latvian
• Lithuanian: lithuanian
• Norwegian (Bokmål): norwegian, light_norwegian, minimal_norwegian
• Norwegian (Nynorsk): light_nynorsk, minimal_nynorsk
• Portuguese: light_portuguese, minimal_portuguese, portuguese, portuguese_rslp
• Romanian: romanian
• Russian: russian, light_russian
• Spanish: light_spanish, spanish
• Swedish: swedish, light_swedish
• Turkish: turkish

You can also use the name parameter as an alias for the language parameter. If both are set, the name parameter is ignored.

Example

The following example request creates a new index named my-stemmer-index and configures an analyzer with a stemmer filter:

PUT /my-stemmer-index
{
  "settings": {
    "analysis": {
      "filter": {
        "my_english_stemmer": {
          "type": "stemmer",
          "language": "english"
        }
      },
      "analyzer": {
        "my_stemmer_analyzer": {
          "type": "custom",
          "tokenizer": "standard",
          "filter": [
            "lowercase",
            "my_english_stemmer"
          ]
        }
      }
    }
  }
}

Generated tokens

Use the following request to examine the tokens generated using the analyzer:

GET /my-stemmer-index/_analyze
{
  "analyzer": "my_stemmer_analyzer",
  "text": "running runs"
}

The response contains the generated tokens:

{
  "tokens": [
    {
      "token": "run",
      "start_offset": 0,
      "end_offset": 7,
      "type": "<ALPHANUM>",
      "position": 0
    },
    {
      "token": "run",
      "start_offset": 8,
      "end_offset": 12,
      "type": "<ALPHANUM>",
      "position": 1
    }
  ]
}