CJK width token filter

Normalizes width differences in CJK (Chinese, Japanese, and Korean) characters as follows:

  • Folds full-width ASCII character variants into the equivalent basic Latin characters
  • Folds half-width Katakana character variants into the equivalent Kana characters

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

This token filter can be viewed as a subset of NFKC/NFKD Unicode normalization. See the analysis-icu plugin for full normalization support.

Example

GET /_analyze
{
  "tokenizer" : "standard",
  "filter" : ["cjk_width"],
  "text" : "シーサイドライナー"
}

The filter produces the following token:

シーサイドライナー

Add to an analyzer

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

PUT /cjk_width_example
{
    "settings" : {
        "analysis" : {
            "analyzer" : {
                "standard_cjk_width" : {
                    "tokenizer" : "standard",
                    "filter" : ["cjk_width"]
                }
            }
        }
    }
}