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Stemmer override token filter

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Stemmer override token filter

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Overrides stemming algorithms, by applying a custom mapping, then protecting these terms from being modified by stemmers. Must be placed before any stemming filters.

Rules are separated by =>

Setting	Description
`rules`	A list of mapping rules to use.
`rules_path`	A path (either relative to `config` location, or absolute) to a list of mappings.

Here is an example:

PUT /my_index
{
    "settings": {
        "analysis" : {
            "analyzer" : {
                "my_analyzer" : {
                    "tokenizer" : "standard",
                    "filter" : ["lowercase", "custom_stems", "porter_stem"]
                }
            },
            "filter" : {
                "custom_stems" : {
                    "type" : "stemmer_override",
                    "rules_path" : "analysis/stemmer_override.txt"
                }
            }
        }
    }
}

Where the file looks like:

running => run

stemmer => stemmer

You can also define the overrides rules inline:

PUT /my_index
{
    "settings": {
        "analysis" : {
            "analyzer" : {
                "my_analyzer" : {
                    "tokenizer" : "standard",
                    "filter" : ["lowercase", "custom_stems", "porter_stem"]
                }
            },
            "filter" : {
                "custom_stems" : {
                    "type" : "stemmer_override",
                    "rules" : [
                        "running => run",
                        "stemmer => stemmer"
                    ]
                }
            }
        }
    }
}

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