Lowercase token filter

Changes token text to lowercase. For example, you can use the lowercase filter to change THE Lazy DoG to the lazy dog.

In addition to a default filter, the lowercase token filter provides access to Lucene’s language-specific lowercase filters for Greek, Irish, and Turkish.

The following analyze API request uses the default lowercase filter to change the THE Quick FoX JUMPs to lowercase:

 GET _analyze {
  "tokenizer" : "standard",
  "filter" : ["lowercase"],
  "text" : "THE Quick FoX JUMPs"
}

The filter produces the following tokens:

[ the, quick, fox, jumps ]

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

 PUT lowercase_example {
  "settings": {
    "analysis": {
      "analyzer": {
        "whitespace_lowercase": {
          "tokenizer": "whitespace",
          "filter": [ "lowercase" ]
        }
      }
    }
  }
}

language

(Optional, string) Language-specific lowercase token filter to use. Valid values include:

greek

Uses Lucene’s GreekLowerCaseFilter

irish

Uses Lucene’s IrishLowerCaseFilter

turkish

Uses Lucene’s TurkishLowerCaseFilter

If not specified, defaults to Lucene’s LowerCaseFilter.

To customize the lowercase 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 lowercase filter for the Greek language:

 PUT custom_lowercase_example {
  "settings": {
    "analysis": {
      "analyzer": {
        "greek_lowercase_example": {
          "type": "custom",
          "tokenizer": "standard",
          "filter": ["greek_lowercase"]
        }
      },
      "filter": {
        "greek_lowercase": {
          "type": "lowercase",
          "language": "greek"
        }
      }
    }
  }
}