Stemmer token filter

Provides algorithmic stemming for several languages, some with additional variants. For a list of supported languages, see the language parameter.

When not customized, the filter uses the porter stemming algorithm for English.

Example

The following analyze API request uses the stemmer filter’s default porter stemming algorithm to stem the foxes jumping quickly to the fox jump quickli:

GET /_analyze
{
  "tokenizer": "standard",
  "filter": [ "stemmer" ],
  "text": "the foxes jumping quickly"
}

The filter produces the following tokens:

[ the, fox, jump, quickli ]

Add to an analyzer

The following create index API request uses the stemmer filter to configure a new custom analyzer.

PUT /my_index
{
  "settings": {
    "analysis": {
      "analyzer": {
        "my_analyzer": {
          "tokenizer": "whitespace",
          "filter": [ "stemmer" ]
        }
      }
    }
  }
}

Configurable parameters

language

(Optional, string) Language-dependent stemming algorithm used to stem tokens. If both this and the name parameter are specified, the language parameter argument is used.

Valid values for language

Valid values are sorted by language. Defaults to english. Recommended algorithms are bolded.

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, 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
name
An alias for the language parameter. If both this and the language parameter are specified, the language parameter argument is used.

Customize

To customize the stemmer filter, duplicate it to create the basis for a new custom token filter. You can modify the filter using its configurable parameters.

For example, the following request creates a custom stemmer filter that stems words using the light_german algorithm:

PUT /my_index
{
  "settings": {
    "analysis": {
      "analyzer": {
        "my_analyzer": {
          "tokenizer": "standard",
          "filter": [
            "lowercase",
            "my_stemmer"
          ]
        }
      },
      "filter": {
        "my_stemmer": {
          "type": "stemmer",
          "language": "light_german"
        }
      }
    }
  }
}