[[analysis-cjk-bigram-tokenfilter]]
=== CJK Bigram Token Filter

The `cjk_bigram` token filter forms bigrams out of the CJK
terms that are generated by the <<analysis-standard-tokenizer,`standard` tokenizer>>
or the `icu_tokenizer` (see <<analysis-icu-plugin>>).

By default, when a CJK character has no adjacent characters to form a bigram,
it is output in unigram form. If you always want to output both unigrams and
bigrams, set the `output_unigrams` flag to `true`. This can be used for a
combined unigram+bigram approach.

Bigrams are generated for characters in `han`, `hiragana`, `katakana` and
`hangul`, but bigrams can be disabled for particular scripts with the
`ignore_scripts` parameter.  All non-CJK input is passed through unmodified.

[source,js]
--------------------------------------------------
{
    "index" : {
        "analysis" : {
            "analyzer" : {
                "han_bigrams" : {
                    "tokenizer" : "standard",
                    "filter" : ["han_bigrams_filter"]
                }
            },
            "filter" : {
                "han_bigrams_filter" : {
                    "type" : "cjk_bigram",
                    "ignore_scripts": [
                        "hiragana",
                        "katakana",
                        "hangul"
                    ],
                    "output_unigrams" : true
                }
            }
        }
    }
}
--------------------------------------------------
