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Elastic Docs ›Elasticsearch Guide [2.0] ›Analysis ›Tokenizers

Edge NGram Tokenizer

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Edge NGram Tokenizer

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A tokenizer of type edgeNGram.

This tokenizer is very similar to nGram but only keeps n-grams which start at the beginning of a token.

The following are settings that can be set for a edgeNGram tokenizer type:

Setting Description Default value

min_gram

Minimum size in codepoints of a single n-gram

1.

max_gram

Maximum size in codepoints of a single n-gram

2.

token_chars

Characters classes to keep in the tokens, Elasticsearch will split on characters that don’t belong to any of these classes.

[] (Keep all characters)

token_chars accepts the following character classes:

letter

for example a, b, ï or 京

digit

for example 3 or 7

whitespace

for example " " or "\n"

punctuation

for example ! or "

symbol

for example $ or √

Example

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    curl -XPUT 'localhost:9200/test' -d '
    {
        "settings" : {
            "analysis" : {
                "analyzer" : {
                    "my_edge_ngram_analyzer" : {
                        "tokenizer" : "my_edge_ngram_tokenizer"
                    }
                },
                "tokenizer" : {
                    "my_edge_ngram_tokenizer" : {
                        "type" : "edgeNGram",
                        "min_gram" : "2",
                        "max_gram" : "5",
                        "token_chars": [ "letter", "digit" ]
                    }
                }
            }
        }
    }'

    curl 'localhost:9200/test/_analyze?pretty=1&analyzer=my_edge_ngram_analyzer' -d 'FC Schalke 04'
    # FC, Sc, Sch, Scha, Schal, 04

side deprecated

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There used to be a side parameter up to 0.90.1 but it is now deprecated. In order to emulate the behavior of "side" : "BACK" a reverse token filter should be used together with the edgeNGram token filter. The edgeNGram filter must be enclosed in reverse filters like this:

    "filter" : ["reverse", "edgeNGram", "reverse"]

which essentially reverses the token, builds front EdgeNGrams and reverses the ngram again. This has the same effect as the previous "side" : "BACK" setting.

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