[[analysis-hunspell-tokenfilter]]
=== Hunspell Token Filter

Basic support for hunspell stemming. Hunspell dictionaries will be
picked up from a dedicated hunspell directory on the filesystem
(`<path.conf>/hunspell`). Each dictionary is expected to
have its own directory named after its associated locale (language).
This dictionary directory is expected to hold a single `*.aff` and
one or more `*.dic` files (all of which will automatically be picked up).
For example, assuming the default hunspell location is used, the
following directory layout will define the `en_US` dictionary:

[source,js]
--------------------------------------------------
- conf
    |-- hunspell
    |    |-- en_US
    |    |    |-- en_US.dic
    |    |    |-- en_US.aff
--------------------------------------------------

Each dictionary can be configured with one setting:

`ignore_case`::
    If true, dictionary matching will be case insensitive
    (defaults to `false`)

This setting can be configured globally in `elasticsearch.yml` using

* `indices.analysis.hunspell.dictionary.ignore_case`

or for specific dictionaries:

* `indices.analysis.hunspell.dictionary.en_US.ignore_case`.

It is also possible to add `settings.yml` file under the dictionary
directory which holds these settings (this will override any other
settings defined in the `elasticsearch.yml`).

One can use the hunspell stem filter by configuring it the analysis
settings:

[source,js]
--------------------------------------------------
{
    "analysis" : {
        "analyzer" : {
            "en" : {
                "tokenizer" : "standard",
                "filter" : [ "lowercase", "en_US" ]
            }
        },
        "filter" : {
            "en_US" : {
                "type" : "hunspell",
                "locale" : "en_US",
                "dedup" : true
            }
        }
    }
}
--------------------------------------------------

The hunspell token filter accepts four options:

`locale`::
    A locale for this filter. If this is unset, the `lang` or
    `language` are used instead - so one of these has to be set.

`dictionary`::
    The name of a dictionary. The path to your hunspell
    dictionaries should be configured via
    `indices.analysis.hunspell.dictionary.location` before.

`dedup`::
    If only unique terms should be returned, this needs to be
    set to `true`. Defaults to `true`.

`longest_only`::
    If only the longest term should be returned, set this to `true`.
    Defaults to `false`: all possible stems are returned.

NOTE: As opposed to the snowball stemmers (which are algorithm based)
this is a dictionary lookup based stemmer and therefore the quality of
the stemming is determined by the quality of the dictionary.

[float]
==== Dictionary loading

By default, the default Hunspell directory (`config/hunspell/`) is checked
for dictionaries when the node starts up, and any dictionaries are
automatically loaded.

Dictionary loading can be deferred until they are actually used by setting
`indices.analysis.hunspell.dictionary.lazy` to `true` in the config file.

[float]
==== References

Hunspell is a spell checker and morphological analyzer designed for
languages with rich morphology and complex word compounding and
character encoding.

1. Wikipedia, http://en.wikipedia.org/wiki/Hunspell

2. Source code, http://hunspell.sourceforge.net/

3. Open Office Hunspell dictionaries, http://wiki.openoffice.org/wiki/Dictionaries

4.  Mozilla Hunspell dictionaries, https://addons.mozilla.org/en-US/firefox/language-tools/

5. Chromium Hunspell dictionaries,
   http://src.chromium.org/viewvc/chrome/trunk/deps/third_party/hunspell_dictionaries/
