Pattern tokenizer

The pattern tokenizer uses a regular expression to either split text into terms whenever it matches a word separator, or to capture matching text as terms.

The default pattern is \W+, which splits text whenever it encounters non-word characters.

 POST _analyze { "tokenizer": "pattern", "text": "The foo_bar_size's default is 5." } 

The above sentence would produce the following terms:

 [ The, foo_bar_size, s, default, is, 5 ] 

The pattern tokenizer accepts the following parameters:

pattern

A Java regular expression, defaults to \W+.

flags

Java regular expression flags. Flags should be pipe-separated, eg "CASE_INSENSITIVE|COMMENTS".

group

Which capture group to extract as tokens. Defaults to -1 (split).

In this example, we configure the pattern tokenizer to break text into tokens when it encounters commas:

 PUT my-index-000001 { "settings": { "analysis": { "analyzer": { "my_analyzer": { "tokenizer": "my_tokenizer" } }, "tokenizer": { "my_tokenizer": { "type": "pattern", "pattern": "," } } } } } POST my-index-000001/_analyze { "analyzer": "my_analyzer", "text": "comma,separated,values" } 

The above example produces the following terms:

 [ comma, separated, values ] 

In the next example, we configure the pattern tokenizer to capture values enclosed in double quotes (ignoring embedded escaped quotes \"). The regex itself looks like this:

 "((?:\\"|[^"]|\\")*)" 

And reads as follows:

• A literal "

• Start capturing:

  • A literal \" OR any character except "
  • Repeat until no more characters match

• A literal closing "

When the pattern is specified in JSON, the " and \ characters need to be escaped, so the pattern ends up looking like:

 \"((?:\\\\\"|[^\"]|\\\\\")+)\" 

 PUT my-index-000001 { "settings": { "analysis": { "analyzer": { "my_analyzer": { "tokenizer": "my_tokenizer" } }, "tokenizer": { "my_tokenizer": { "type": "pattern", "pattern": "\"((?:\\\\\"|[^\"]|\\\\\")+)\"", "group": 1 } } } } } POST my-index-000001/_analyze { "analyzer": "my_analyzer", "text": "\"value\", \"value with embedded \\\" quote\"" } 

The above example produces the following two terms:

 [ value, value with embedded \" quote ]