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add kstem token filter docs #8150 (#8473)
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* add kstem token filter docs #8150

Signed-off-by: Anton Rubin <[email protected]>

* Doc review

Signed-off-by: Fanit Kolchina <[email protected]>

* Apply suggestions from code review

Co-authored-by: Nathan Bower <[email protected]>
Signed-off-by: kolchfa-aws <[email protected]>

---------

Signed-off-by: Anton Rubin <[email protected]>
Signed-off-by: Fanit Kolchina <[email protected]>
Signed-off-by: kolchfa-aws <[email protected]>
Co-authored-by: Fanit Kolchina <[email protected]>
Co-authored-by: kolchfa-aws <[email protected]>
Co-authored-by: Nathan Bower <[email protected]>
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2 changes: 1 addition & 1 deletion _analyzers/token-filters/index.md
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Expand Up @@ -36,7 +36,7 @@ Token filter | Underlying Lucene token filter| Description
[`keep_words`]({{site.url}}{{site.baseurl}}/analyzers/token-filters/keep-words/) | [KeepWordFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/miscellaneous/KeepWordFilter.html) | Checks the tokens against the specified word list and keeps only those that are in the list.
[`keyword_marker`]({{site.url}}{{site.baseurl}}/analyzers/token-filters/keyword-marker/) | [KeywordMarkerFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/miscellaneous/KeywordMarkerFilter.html) | Marks specified tokens as keywords, preventing them from being stemmed.
`keyword_repeat` | [KeywordRepeatFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/miscellaneous/KeywordRepeatFilter.html) | Emits each incoming token twice: once as a keyword and once as a non-keyword.
`kstem` | [KStemFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/en/KStemFilter.html) | Provides kstem-based stemming for the English language. Combines algorithmic stemming with a built-in dictionary.
[`kstem`]({{site.url}}{{site.baseurl}}/analyzers/token-filters/kstem/) | [KStemFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/en/KStemFilter.html) | Provides KStem-based stemming for the English language. Combines algorithmic stemming with a built-in dictionary.
`kuromoji_completion` | [JapaneseCompletionFilter](https://lucene.apache.org/core/9_10_0/analysis/kuromoji/org/apache/lucene/analysis/ja/JapaneseCompletionFilter.html) | Adds Japanese romanized terms to the token stream (in addition to the original tokens). Usually used to support autocomplete on Japanese search terms. Note that the filter has a `mode` parameter, which should be set to `index` when used in an index analyzer and `query` when used in a search analyzer. Requires the `analysis-kuromoji` plugin. For information about installing the plugin, see [Additional plugins]({{site.url}}{{site.baseurl}}/install-and-configure/plugins/#additional-plugins).
[`length`]({{site.url}}{{site.baseurl}}/analyzers/token-filters/length/) | [LengthFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/miscellaneous/LengthFilter.html) | Removes tokens that are shorter or longer than the length range specified by `min` and `max`.
[`limit`]({{site.url}}{{site.baseurl}}/analyzers/token-filters/limit/) | [LimitTokenCountFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/miscellaneous/LimitTokenCountFilter.html) | Limits the number of output tokens. For example, document field value sizes can be limited based on the token count.
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92 changes: 92 additions & 0 deletions _analyzers/token-filters/kstem.md
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---
layout: default
title: KStem
parent: Token filters
nav_order: 220
---

# KStem token filter

The `kstem` token filter is a stemming filter used to reduce words to their root forms. The filter is a lightweight algorithmic stemmer designed for the English language that performs the following stemming operations:

- Reduces plurals to their singular form.
- Converts different verb tenses to their base form.
- Removes common derivational endings, such as "-ing" or "-ed".

The `kstem` token filter is equivalent to the a `stemmer` filter configured with a `light_english` language. It provides a more conservative stemming compared to other stemming filters like `porter_stem`.

The `kstem` token filter is based on the Lucene KStemFilter. For more information, see the [Lucene documentation](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/en/KStemFilter.html).

## Example

The following example request creates a new index named `my_kstem_index` and configures an analyzer with a `kstem` filter:

```json
PUT /my_kstem_index
{
"settings": {
"analysis": {
"filter": {
"kstem_filter": {
"type": "kstem"
}
},
"analyzer": {
"my_kstem_analyzer": {
"type": "custom",
"tokenizer": "standard",
"filter": [
"lowercase",
"kstem_filter"
]
}
}
}
},
"mappings": {
"properties": {
"content": {
"type": "text",
"analyzer": "my_kstem_analyzer"
}
}
}
}
```
{% include copy-curl.html %}

## Generated tokens

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

```json
POST /my_kstem_index/_analyze
{
"analyzer": "my_kstem_analyzer",
"text": "stops stopped"
}
```
{% include copy-curl.html %}

The response contains the generated tokens:

```json
{
"tokens": [
{
"token": "stop",
"start_offset": 0,
"end_offset": 5,
"type": "<ALPHANUM>",
"position": 0
},
{
"token": "stop",
"start_offset": 6,
"end_offset": 13,
"type": "<ALPHANUM>",
"position": 1
}
]
}
```

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