CJK width token filter
The cjk_width
token filter normalizes Chinese, Japanese, and Korean (CJK) tokens by converting full-width ASCII characters to their standard (half-width) ASCII equivalents and half-width katakana characters to their full-width equivalents.
Converting full-width ASCII characters
In CJK texts, ASCII characters (such as letters and numbers) can appear in full-width form, occupying the space of two half-width characters. Full-width ASCII characters are typically used in East Asian typography for alignment with the width of CJK characters. However, for the purposes of indexing and searching, these full-width characters need to be normalized to their standard (half-width) ASCII equivalents.
The following example illustrates ASCII character normalization:
Full-Width: ABCDE 12345
Normalized (half-width): ABCDE 12345
Converting half-width katakana characters
The cjk_width
token filter converts half-width katakana characters to their full-width counterparts, which are the standard form used in Japanese text. This normalization, illustrated in the following example, is important for consistency in text processing and searching:
Half-Width katakana: カタカナ
Normalized (full-width) katakana: カタカナ
Example
The following example request creates a new index named cjk_width_example_index
and defines an analyzer with the cjk_width
filter:
PUT /cjk_width_example_index
{
"settings": {
"analysis": {
"analyzer": {
"cjk_width_analyzer": {
"type": "custom",
"tokenizer": "standard",
"filter": ["cjk_width"]
}
}
}
}
}
Generated tokens
Use the following request to examine the tokens generated using the analyzer:
POST /cjk_width_example_index/_analyze
{
"analyzer": "cjk_width_analyzer",
"text": "Tokyo 2024 カタカナ"
}
The response contains the generated tokens:
{
"tokens": [
{
"token": "Tokyo",
"start_offset": 0,
"end_offset": 5,
"type": "<ALPHANUM>",
"position": 0
},
{
"token": "2024",
"start_offset": 6,
"end_offset": 10,
"type": "<NUM>",
"position": 1
},
{
"token": "カタカナ",
"start_offset": 11,
"end_offset": 15,
"type": "<KATAKANA>",
"position": 2
}
]
}