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Add lowercase token filter docs #8162

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Dec 2, 2024
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Add lowercase token filter docs #8162

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5dddda8
add lowercase token filter
AntonEliatra Sep 3, 2024
167d063
adding examples in greek to lowercase token filter #8154
AntonEliatra Sep 3, 2024
9a46d9a
Update lowercase.md
AntonEliatra Sep 12, 2024
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Doc review
kolchfa-aws Nov 15, 2024
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kolchfa-aws Dec 2, 2024
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Merge branch 'main' into add-lowercase-token-filter-docs
kolchfa-aws Dec 2, 2024
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2 changes: 1 addition & 1 deletion _analyzers/token-filters/index.md
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Expand Up @@ -38,7 +38,7 @@ Token filter | Underlying Lucene token filter| Description
`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` | [LengthFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/miscellaneous/LengthFilter.html) | Removes tokens whose lengths are shorter or longer than the length range specified by `min` and `max`.
`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. A common use case is to limit the size of document field values based on token count.
`lowercase` | [LowerCaseFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/core/LowerCaseFilter.html) | Converts tokens to lowercase. The default [LowerCaseFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/core/LowerCaseFilter.html) is for the English language. You can set the `language` parameter to `greek` (uses [GreekLowerCaseFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/el/GreekLowerCaseFilter.html)), `irish` (uses [IrishLowerCaseFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/ga/IrishLowerCaseFilter.html)), or `turkish` (uses [TurkishLowerCaseFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/tr/TurkishLowerCaseFilter.html)).
[`lowercase`]({{site.url}}{{site.baseurl}}/analyzers/token-filters/lowercase/) | [LowerCaseFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/core/LowerCaseFilter.html) | Converts tokens to lowercase. The default [LowerCaseFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/core/LowerCaseFilter.html) is for the English language. You can set the `language` parameter to `greek` (uses [GreekLowerCaseFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/el/GreekLowerCaseFilter.html)), `irish` (uses [IrishLowerCaseFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/ga/IrishLowerCaseFilter.html)), or `turkish` (uses [TurkishLowerCaseFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/tr/TurkishLowerCaseFilter.html)).
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`min_hash` | [MinHashFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/minhash/MinHashFilter.html) | Uses the [MinHash technique](https://en.wikipedia.org/wiki/MinHash) to estimate document similarity. Performs the following operations on a token stream sequentially: <br> 1. Hashes each token in the stream. <br> 2. Assigns the hashes to buckets, keeping only the smallest hashes of each bucket. <br> 3. Outputs the smallest hash from each bucket as a token stream.
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Line 41: Confirm the accuracy of my changes.

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Not quite: the default specifies no language and processes English. There are also a couple of other language options. Reworded.

`multiplexer` | N/A | Emits multiple tokens at the same position. Runs each token through each of the specified filter lists separately and outputs the results as separate tokens.
`ngram` | [NGramTokenFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/ngram/NGramTokenFilter.html) | Tokenizes the given token into n-grams of lengths between `min_gram` and `max_gram`.
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82 changes: 82 additions & 0 deletions _analyzers/token-filters/lowercase.md
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@@ -0,0 +1,82 @@
---
layout: default
title: Lowercase
parent: Token filters
nav_order: 260
---

# Lowercase token filter

The `lowercase` token filter is used to convert all characters in the token stream to lowercase, making searches case insensitive.

## Parameters

The `lowercase` token filter can be configured with the following parameter.

Parameter | Required/Optional | Description
:--- | :--- | :---
`language` | Optional | Specifies a language-specific token filter to use for lowercasing. Valid values are: <br>- [`greek`](https://lucene.apache.org/core/8_7_0/analyzers-common/org/apache/lucene/analysis/el/GreekLowerCaseFilter.html) <br>- [`irish`](https://lucene.apache.org/core/8_7_0/analyzers-common/org/apache/lucene/analysis/ga/IrishLowerCaseFilter.html) <br>- [`turkish`](https://lucene.apache.org/core/8_7_0/analyzers-common/org/apache/lucene/analysis/tr/TurkishLowerCaseFilter.html). <br> Default is [Lucene’s LowerCaseFilter](https://lucene.apache.org/core/8_7_0/analyzers-common/org/apache/lucene/analysis/core/LowerCaseFilter.html).

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[OpenSearch.Spelling] Error: lowercasing. If you are referencing a setting, variable, format, function, or repository, surround it with tic marks.

Raw Output:
{"message": "[OpenSearch.Spelling] Error: lowercasing. If you are referencing a setting, variable, format, function, or repository, surround it with tic marks.", "location": {"path": "_analyzers/token-filters/lowercase.md", "range": {"start": {"line": 18, "column": 80}}}, "severity": "ERROR"}
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Line 18: Is english also an option, or is that the default used by the Lucene filter?

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Default without specifying a language.

## Example

The following example request creates a new index named `custom_lowercase_example`. It configures an analyzer with a `lowercase` filter and specifies `greek` as the `language`:

```json
PUT /custom_lowercase_example
{
"settings": {
"analysis": {
"analyzer": {
"greek_lowercase_example": {
"type": "custom",
"tokenizer": "standard",
"filter": ["greek_lowercase"]
}
},
"filter": {
"greek_lowercase": {
"type": "lowercase",
"language": "greek"
}
}
}
}
}
```
{% include copy-curl.html %}

## Generated tokens

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

```json
GET /custom_lowercase_example/_analyze
{
"analyzer": "greek_lowercase_example",
"text": "Αθήνα ΕΛΛΑΔΑ"
}
```
{% include copy-curl.html %}

The response contains the generated tokens:

```json
{
"tokens": [
{
"token": "αθηνα",
"start_offset": 0,
"end_offset": 5,
"type": "<ALPHANUM>",
"position": 0
},
{
"token": "ελλαδα",
"start_offset": 6,
"end_offset": 12,
"type": "<ALPHANUM>",
"position": 1
}
]
}
```
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