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Trim token filter

Removes leading and trailing whitespace from each token in a stream. While this can change the length of a token, the trim filter does not change a token’s offsets.

The trim filter uses Lucene’s TrimFilter.

Many commonly used tokenizers, such as the standard or whitespace tokenizer, remove whitespace by default. When using these tokenizers, you don’t need to add a separate trim filter.

Example

To see how the trim filter works, you first need to produce a token containing whitespace.

The following analyze API request uses the keyword tokenizer to produce a token for " fox ".

GET _analyze
{
  "tokenizer" : "keyword",
  "text" : " fox "
}

The API returns the following response. Note the " fox " token contains the original text’s whitespace. Note that despite changing the token’s length, the start_offset and end_offset remain the same.

{
  "tokens": [
    {
      "token": " fox ",
      "start_offset": 0,
      "end_offset": 5,
      "type": "word",
      "position": 0
    }
  ]
}

To remove the whitespace, add the trim filter to the previous analyze API request.

GET _analyze
{
  "tokenizer" : "keyword",
  "filter" : ["trim"],
  "text" : " fox "
}

The API returns the following response. The returned fox token does not include any leading or trailing whitespace.

{
  "tokens": [
    {
      "token": "fox",
      "start_offset": 0,
      "end_offset": 5,
      "type": "word",
      "position": 0
    }
  ]
}

Add to an analyzer

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

PUT trim_example
{
  "settings": {
    "analysis": {
      "analyzer": {
        "keyword_trim": {
          "tokenizer": "keyword",
          "filter": [ "trim" ]
        }
      }
    }
  }
}

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https://www.elastic.co/guide/en/elasticsearch/reference/7.17/analysis-trim-tokenfilter.html