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Truncate token filter

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Truncate token filter

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Truncates tokens that exceed a specified character limit. This limit defaults to 10 but can be customized using the length parameter.

For example, you can use the truncate filter to shorten all tokens to 3 characters or fewer, changing jumping fox to jum fox.

This filter uses Lucene’s TruncateTokenFilter.

Example

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The following analyze API request uses the truncate filter to shorten tokens that exceed 10 characters in the quinquennial extravaganza carried on:

response = client.indices.analyze(
  body: {
    tokenizer: 'whitespace',
    filter: [
      'truncate'
    ],
    text: 'the quinquennial extravaganza carried on'
  }
)
puts response

GET _analyze
{
  "tokenizer" : "whitespace",
  "filter" : ["truncate"],
  "text" : "the quinquennial extravaganza carried on"
}

The filter produces the following tokens:

[ the, quinquenni, extravagan, carried, on ]

Add to an analyzer

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

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

PUT custom_truncate_example
{
  "settings" : {
    "analysis" : {
      "analyzer" : {
        "standard_truncate" : {
        "tokenizer" : "standard",
        "filter" : ["truncate"]
        }
      }
    }
  }
}

Configurable parameters

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length: (Optional, integer) Character limit for each token. Tokens exceeding this limit are truncated. Defaults to 10.

Customize

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

For example, the following request creates a custom truncate filter, 5_char_trunc, that shortens tokens to a length of 5 or fewer characters:

response = client.indices.create(
  index: '5_char_words_example',
  body: {
    settings: {
      analysis: {
        analyzer: {
          "lowercase_5_char": {
            tokenizer: 'lowercase',
            filter: [
              '5_char_trunc'
            ]
          }
        },
        filter: {
          "5_char_trunc": {
            type: 'truncate',
            length: 5
          }
        }
      }
    }
  }
)
puts response

PUT 5_char_words_example
{
  "settings": {
    "analysis": {
      "analyzer": {
        "lowercase_5_char": {
          "tokenizer": "lowercase",
          "filter": [ "5_char_trunc" ]
        }
      },
      "filter": {
        "5_char_trunc": {
          "type": "truncate",
          "length": 5
        }
      }
    }
  }
}

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