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

slug	sidebar_position	sidebar_label
/en/sql-reference/functions/nlp-functions	130	NLP (experimental)

Natural Language Processing (NLP) Functions

:::note 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. Use the two letter ISO 639-1 code.
• 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'] │
└────────────────────────────────────────────────────┘

Supported languages for stem()

:::note The stem() function uses the Snowball stemming library, see the Snowball website for updated languages etc. :::

• Arabic
• Armenian
• Basque
• Catalan
• Danish
• Dutch
• English
• Finnish
• French
• German
• Greek
• Hindi
• Hungarian
• Indonesian
• Irish
• Italian
• Lithuanian
• Nepali
• Norwegian
• Porter
• Portuguese
• Romanian
• Russian
• Serbian
• Spanish
• Swedish
• Tamil
• Turkish
• Yiddish

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

This configuration specifies that the dictionary en.bin should be used for lemmatization of English (en) words. The .bin files can be downloaded from here.

<lemmatizers>
    <lemmatizer>
        <!-- highlight-start -->
        <lang>en</lang>
        <path>en.bin</path>
        <!-- highlight-end -->
    </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>

detectLanguage

Detects the language of the UTF8-encoded input string. The function uses the CLD2 library for detection, and it returns the 2-letter ISO language code.

The detectLanguage function works best when providing over 200 characters in the input string.

Syntax

detectLanguage('text_to_be_analyzed')

Arguments

• text_to_be_analyzed — A collection (or sentences) of strings to analyze. String.

Returned value

• The 2-letter ISO code of the detected language

Other possible results:

• un = unknown, can not detect any language.
• other = the detected language does not have 2 letter code.

Examples

Query:

SELECT detectLanguage('Je pense que je ne parviendrai jamais à parler français comme un natif. Where there’s a will, there’s a way.');

Result:

fr

detectLanguageMixed

Similar to the detectLanguage function, but detectLanguageMixed returns a Map of 2-letter language codes that are mapped to the percentage of the certain language in the text.

Syntax

detectLanguageMixed('text_to_be_analyzed')

Arguments

• text_to_be_analyzed — A collection (or sentences) of strings to analyze. String.

Returned value

• Map(String, Float32): The keys are 2-letter ISO codes and the values are a percentage of text found for that language

Examples

Query:

SELECT detectLanguageMixed('二兎を追う者は一兎をも得ず二兎を追う者は一兎をも得ず A vaincre sans peril, on triomphe sans gloire.');

Result:

┌─detectLanguageMixed()─┐
│ {'ja':0.62,'fr':0.36  │
└───────────────────────┘

detectLanguageUnknown

Similar to the detectLanguage function, except the detectLanguageUnknown function works with non-UTF8-encoded strings. Prefer this version when your character set is UTF-16 or UTF-32.

Syntax

detectLanguageUnknown('text_to_be_analyzed')

Arguments

• text_to_be_analyzed — A collection (or sentences) of strings to analyze. String.

Returned value

• The 2-letter ISO code of the detected language

Other possible results:

• un = unknown, can not detect any language.
• other = the detected language does not have 2 letter code.

Examples

Query:

SELECT detectLanguageUnknown('Ich bleibe für ein paar Tage.');

Result:

┌─detectLanguageUnknown('Ich bleibe für ein paar Tage.')─┐
│ de                                                     │
└────────────────────────────────────────────────────────┘

detectCharset

The detectCharset function detects the character set of the non-UTF8-encoded input string.

Syntax

detectCharset('text_to_be_analyzed')

Arguments

• text_to_be_analyzed — A collection (or sentences) of strings to analyze. String.

Returned value

• A String containing the code of the detected character set

Examples

Query:

SELECT detectCharset('Ich bleibe für ein paar Tage.');

Result:

┌─detectCharset('Ich bleibe für ein paar Tage.')─┐
│ WINDOWS-1252                                   │
└────────────────────────────────────────────────┘