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4 | 4 | <titleabbrev>Reverse</titleabbrev>
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5 | 5 | ++++
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6 | 6 |
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7 |
| -A token filter of type `reverse` that simply reverses each token. |
| 7 | +Reverses each token in a stream. For example, you can use the `reverse` filter |
| 8 | +to change `cat` to `tac`. |
| 9 | + |
| 10 | +Reversed tokens are useful for suffix-based searches, |
| 11 | +such as finding words that end in `-ion` or searching file names by their |
| 12 | +extension. |
| 13 | + |
| 14 | +This filter uses Lucene's |
| 15 | +https://lucene.apache.org/core/{lucene_version_path}/analyzers-common/org/apache/lucene/analysis/reverse/ReverseStringFilter.html[ReverseStringFilter]. |
| 16 | + |
| 17 | +[[analysis-reverse-tokenfilter-analyze-ex]] |
| 18 | +==== Example |
| 19 | + |
| 20 | +The following <<indices-analyze,analyze API>> request uses the `reverse` |
| 21 | +filter to reverse each token in `quick fox jumps`: |
| 22 | + |
| 23 | +[source,console] |
| 24 | +-------------------------------------------------- |
| 25 | +GET _analyze |
| 26 | +{ |
| 27 | + "tokenizer" : "standard", |
| 28 | + "filter" : ["reverse"], |
| 29 | + "text" : "quick fox jumps" |
| 30 | +} |
| 31 | +-------------------------------------------------- |
| 32 | + |
| 33 | +The filter produces the following tokens: |
| 34 | + |
| 35 | +[source,text] |
| 36 | +-------------------------------------------------- |
| 37 | +[ kciuq, xof, spmuj ] |
| 38 | +-------------------------------------------------- |
| 39 | + |
| 40 | +///////////////////// |
| 41 | +[source,console-result] |
| 42 | +-------------------------------------------------- |
| 43 | +{ |
| 44 | + "tokens" : [ |
| 45 | + { |
| 46 | + "token" : "kciuq", |
| 47 | + "start_offset" : 0, |
| 48 | + "end_offset" : 5, |
| 49 | + "type" : "<ALPHANUM>", |
| 50 | + "position" : 0 |
| 51 | + }, |
| 52 | + { |
| 53 | + "token" : "xof", |
| 54 | + "start_offset" : 6, |
| 55 | + "end_offset" : 9, |
| 56 | + "type" : "<ALPHANUM>", |
| 57 | + "position" : 1 |
| 58 | + }, |
| 59 | + { |
| 60 | + "token" : "spmuj", |
| 61 | + "start_offset" : 10, |
| 62 | + "end_offset" : 15, |
| 63 | + "type" : "<ALPHANUM>", |
| 64 | + "position" : 2 |
| 65 | + } |
| 66 | + ] |
| 67 | +} |
| 68 | +-------------------------------------------------- |
| 69 | +///////////////////// |
| 70 | + |
| 71 | +[[analysis-reverse-tokenfilter-analyzer-ex]] |
| 72 | +==== Add to an analyzer |
| 73 | + |
| 74 | +The following <<indices-create-index,create index API>> request uses the |
| 75 | +`reverse` filter to configure a new |
| 76 | +<<analysis-custom-analyzer,custom analyzer>>. |
| 77 | + |
| 78 | +[source,console] |
| 79 | +-------------------------------------------------- |
| 80 | +PUT reverse_example |
| 81 | +{ |
| 82 | + "settings" : { |
| 83 | + "analysis" : { |
| 84 | + "analyzer" : { |
| 85 | + "whitespace_reverse" : { |
| 86 | + "tokenizer" : "whitespace", |
| 87 | + "filter" : ["reverse"] |
| 88 | + } |
| 89 | + } |
| 90 | + } |
| 91 | + } |
| 92 | +} |
| 93 | +-------------------------------------------------- |
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