ClickHouse/docs/en/sql-reference/functions/nlp-functions.md

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---
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slug: /en/sql-reference/functions/nlp-functions
sidebar_position: 67
sidebar_label: NLP
---
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# [experimental] Natural Language Processing functions
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:::warning
This is an experimental feature that is currently in development and is not ready for general use. It will change in unpredictable backwards-incompatible ways in future releases. Set `allow_experimental_nlp_functions = 1` to enable it.
:::
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## stem
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Performs stemming on a given word.
**Syntax**
``` sql
stem('language', word)
```
**Arguments**
- `language` — Language which rules will be applied. Must be in lowercase. [String](../../sql-reference/data-types/string.md#string).
- `word` — word that needs to be stemmed. Must be in lowercase. [String](../../sql-reference/data-types/string.md#string).
**Examples**
Query:
``` sql
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SELECT arrayMap(x -> stem('en', x), ['I', 'think', 'it', 'is', 'a', 'blessing', 'in', 'disguise']) as res;
```
Result:
``` text
┌─res────────────────────────────────────────────────┐
│ ['I','think','it','is','a','bless','in','disguis'] │
└────────────────────────────────────────────────────┘
```
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## lemmatize
Performs lemmatization on a given word. Needs dictionaries to operate, which can be obtained [here](https://github.com/vpodpecan/lemmagen3/tree/master/src/lemmagen3/models).
**Syntax**
``` sql
lemmatize('language', word)
```
**Arguments**
- `language` — Language which rules will be applied. [String](../../sql-reference/data-types/string.md#string).
- `word` — Word that needs to be lemmatized. Must be lowercase. [String](../../sql-reference/data-types/string.md#string).
**Examples**
Query:
``` sql
SELECT lemmatize('en', 'wolves');
```
Result:
``` text
┌─lemmatize("wolves")─┐
│ "wolf" │
└─────────────────────┘
```
Configuration:
``` xml
<lemmatizers>
<lemmatizer>
<lang>en</lang>
<path>en.bin</path>
</lemmatizer>
</lemmatizers>
```
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## synonyms
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Finds synonyms to a given word. There are two types of synonym extensions: `plain` and `wordnet`.
With the `plain` extension type we need to provide a path to a simple text file, where each line corresponds to a certain synonym set. Words in this line must be separated with space or tab characters.
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With the `wordnet` extension type we need to provide a path to a directory with WordNet thesaurus in it. Thesaurus must contain a WordNet sense index.
**Syntax**
``` sql
synonyms('extension_name', word)
```
**Arguments**
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- `extension_name` — Name of the extension in which search will be performed. [String](../../sql-reference/data-types/string.md#string).
- `word` — Word that will be searched in extension. [String](../../sql-reference/data-types/string.md#string).
**Examples**
Query:
``` sql
SELECT synonyms('list', 'important');
```
Result:
``` text
┌─synonyms('list', 'important')────────────┐
│ ['important','big','critical','crucial'] │
└──────────────────────────────────────────┘
```
Configuration:
``` xml
<synonyms_extensions>
<extension>
<name>en</name>
<type>plain</type>
<path>en.txt</path>
</extension>
<extension>
<name>en</name>
<type>wordnet</type>
<path>en/</path>
</extension>
</synonyms_extensions>
```