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CJK bigram token filter

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CJK bigram token filter

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Forms bigrams out of CJK (Chinese, Japanese, and Korean) tokens.

This filter is included in Elasticsearch’s built-in CJK language analyzer. It uses Lucene’s CJKBigramFilter.

Example

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The following analyze API request demonstrates how the CJK bigram token filter works.

response = client.indices.analyze(
  body: {
    tokenizer: 'standard',
    filter: [
      'cjk_bigram'
    ],
    text: '東京都は、日本の首都であり'
  }
)
puts response

GET /_analyze
{
  "tokenizer" : "standard",
  "filter" : ["cjk_bigram"],
  "text" : "東京都は、日本の首都であり"
}

The filter produces the following tokens:

[ 東京, 京都, 都は, 日本, 本の, の首, 首都, 都で, であ, あり ]

Add to an analyzer

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The following create index API request uses the CJK bigram token filter to configure a new custom analyzer.

response = client.indices.create(
  index: 'cjk_bigram_example',
  body: {
    settings: {
      analysis: {
        analyzer: {
          standard_cjk_bigram: {
            tokenizer: 'standard',
            filter: [
              'cjk_bigram'
            ]
          }
        }
      }
    }
  }
)
puts response

PUT /cjk_bigram_example
{
  "settings": {
    "analysis": {
      "analyzer": {
        "standard_cjk_bigram": {
          "tokenizer": "standard",
          "filter": [ "cjk_bigram" ]
        }
      }
    }
  }
}

Configurable parameters

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ignored_scripts

(Optional, array of character scripts) Array of character scripts for which to disable bigrams. Possible values:

han
hangul
hiragana
katakana

All non-CJK input is passed through unmodified.

output_unigrams

(Optional, Boolean) If true, emit tokens in both bigram and unigram form. If false, a CJK character is output in unigram form when it has no adjacent characters. Defaults to false.

Customize

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To customize the CJK bigram token filter, duplicate it to create the basis for a new custom token filter. You can modify the filter using its configurable parameters.

PUT /cjk_bigram_example
{
  "settings": {
    "analysis": {
      "analyzer": {
        "han_bigrams": {
          "tokenizer": "standard",
          "filter": [ "han_bigrams_filter" ]
        }
      },
      "filter": {
        "han_bigrams_filter": {
          "type": "cjk_bigram",
          "ignored_scripts": [
            "hangul",
            "hiragana",
            "katakana"
          ],
          "output_unigrams": true
        }
      }
    }
  }
}

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