[[analysis-pattern-analyzer]]
=== Pattern Analyzer

An analyzer of type `pattern` that can flexibly separate text into terms
via a regular expression. Accepts the following settings:

The following are settings that can be set for a `pattern` analyzer
type:

[cols="<,<",options="header",]
|===================================================================
|Setting |Description
|`lowercase` |Should terms be lowercased or not. Defaults to `true`.
|`pattern` |The regular expression pattern, defaults to `\W+`.
|`flags` |The regular expression flags.
|`stopwords` |A list of stopwords to initialize the stop filter with.
Defaults to an 'empty' stopword list added[1.0.0.RC1, Previously 
defaulted to the English stopwords list]. Check
<<analysis-stop-analyzer,Stop Analyzer>> for more details.
|===================================================================

*IMPORTANT*: The regular expression should match the *token separators*,
not the tokens themselves.

Flags should be pipe-separated, eg `"CASE_INSENSITIVE|COMMENTS"`. Check
http://download.oracle.com/javase/6/docs/api/java/util/regex/Pattern.html#field_summary[Java
Pattern API] for more details about `flags` options.

[float]
==== Pattern Analyzer Examples

In order to try out these examples, you should delete the `test` index
before running each example:

[source,js]
--------------------------------------------------
    curl -XDELETE localhost:9200/test
--------------------------------------------------

[float]
===== Whitespace tokenizer

[source,js]
--------------------------------------------------
    curl -XPUT 'localhost:9200/test' -d '
    {
        "settings":{
            "analysis": {
                "analyzer": {
                    "whitespace":{
                        "type": "pattern",
                        "pattern":"\\\\s+"
                    }
                }
            }
        }
    }'

    curl 'localhost:9200/test/_analyze?pretty=1&analyzer=whitespace' -d 'foo,bar baz'
    # "foo,bar", "baz"
--------------------------------------------------

[float]
===== Non-word character tokenizer

[source,js]
--------------------------------------------------

    curl -XPUT 'localhost:9200/test' -d '
    {
        "settings":{
            "analysis": {
                "analyzer": {
                    "nonword":{
                        "type": "pattern",
                        "pattern":"[^\\\\w]+"
                    }
                }
            }
        }
    }'

    curl 'localhost:9200/test/_analyze?pretty=1&analyzer=nonword' -d 'foo,bar baz'
    # "foo,bar baz" becomes "foo", "bar", "baz"

    curl 'localhost:9200/test/_analyze?pretty=1&analyzer=nonword' -d 'type_1-type_4'
    # "type_1","type_4"
--------------------------------------------------

[float]
===== CamelCase tokenizer

[source,js]
--------------------------------------------------

    curl -XPUT 'localhost:9200/test?pretty=1' -d '
    {
        "settings":{
            "analysis": {
                "analyzer": {
                    "camel":{
                        "type": "pattern",
                        "pattern":"([^\\\\p{L}\\\\d]+)|(?<=\\\\D)(?=\\\\d)|(?<=\\\\d)(?=\\\\D)|(?<=[\\\\p{L}&&[^\\\\p{Lu}]])(?=\\\\p{Lu})|(?<=\\\\p{Lu})(?=\\\\p{Lu}[\\\\p{L}&&[^\\\\p{Lu}]])"
                    }
                }
            }
        }
    }'

    curl 'localhost:9200/test/_analyze?pretty=1&analyzer=camel' -d '
        MooseX::FTPClass2_beta
    '
    # "moose","x","ftp","class","2","beta"
--------------------------------------------------

The regex above is easier to understand as:

[source,js]
--------------------------------------------------

      ([^\\p{L}\\d]+)                 # swallow non letters and numbers,
    | (?<=\\D)(?=\\d)                 # or non-number followed by number,
    | (?<=\\d)(?=\\D)                 # or number followed by non-number,
    | (?<=[ \\p{L} && [^\\p{Lu}]])    # or lower case
      (?=\\p{Lu})                    #   followed by upper case,
    | (?<=\\p{Lu})                   # or upper case
      (?=\\p{Lu}                     #   followed by upper case
        [\\p{L}&&[^\\p{Lu}]]          #   then lower case
      )
--------------------------------------------------
