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

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67	NLP

[experimental] Natural Language Processing functions

:::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. :::

stem

Performs stemming on a given word.

Syntax

stem('language', word)

Arguments

• language — Language which rules will be applied. Must be in lowercase. String.
• word — word that needs to be stemmed. Must be in lowercase. String.

Examples

Query:

SELECT arrayMap(x -> stem('en', x), ['I', 'think', 'it', 'is', 'a', 'blessing', 'in', 'disguise']) as res;

Result:

┌─res────────────────────────────────────────────────┐
│ ['I','think','it','is','a','bless','in','disguis'] │
└────────────────────────────────────────────────────┘

lemmatize

Performs lemmatization on a given word. Needs dictionaries to operate, which can be obtained here.

Syntax

lemmatize('language', word)

Arguments

• language — Language which rules will be applied. String.
• word — Word that needs to be lemmatized. Must be lowercase. String.

Examples

Query:

SELECT lemmatize('en', 'wolves');

Result:

┌─lemmatize("wolves")─┐
│              "wolf" │
└─────────────────────┘

Configuration:

<lemmatizers>
    <lemmatizer>
        <lang>en</lang>
        <path>en.bin</path>
    </lemmatizer>
</lemmatizers>

synonyms

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.

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

synonyms('extension_name', word)

Arguments

• extension_name — Name of the extension in which search will be performed. String.
• word — Word that will be searched in extension. String.

Examples

Query:

SELECT synonyms('list', 'important');

Result:

┌─synonyms('list', 'important')────────────┐
│ ['important','big','critical','crucial'] │
└──────────────────────────────────────────┘

Configuration:

<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>