Remove duplicates token filter

Removes duplicate tokens in the same position.

The remove_duplicates filter uses Lucene’s RemoveDuplicatesTokenFilter.

Example

To see how the remove_duplicates filter works, you first need to produce a token stream containing duplicate tokens in the same position.

The following analyze API request uses the keyword_repeat and stemmer filters to create stemmed and unstemmed tokens for jumping dog.

  1. GET _analyze
  2. {
  3.   "tokenizer": "whitespace",
  4.   "filter": [
  5.     "keyword_repeat",
  6.     "stemmer"
  7.   ],
  8.   "text": "jumping dog"
  9. }

The API returns the following response. Note that the dog token in position 1 is duplicated.

  1. {
  2.   "tokens": [
  3.     {
  4.       "token": "jumping",
  5.       "start_offset": 0,
  6.       "end_offset": 7,
  7.       "type": "word",
  8.       "position": 0
  9.     },
  10.     {
  11.       "token": "jump",
  12.       "start_offset": 0,
  13.       "end_offset": 7,
  14.       "type": "word",
  15.       "position": 0
  16.     },
  17.     {
  18.       "token": "dog",
  19.       "start_offset": 8,
  20.       "end_offset": 11,
  21.       "type": "word",
  22.       "position": 1
  23.     },
  24.     {
  25.       "token": "dog",
  26.       "start_offset": 8,
  27.       "end_offset": 11,
  28.       "type": "word",
  29.       "position": 1
  30.     }
  31.   ]
  32. }

To remove one of the duplicate dog tokens, add the remove_duplicates filter to the previous analyze API request.

  1. GET _analyze
  2. {
  3.   "tokenizer": "whitespace",
  4.   "filter": [
  5.     "keyword_repeat",
  6.     "stemmer",
  7.     "remove_duplicates"
  8.   ],
  9.   "text": "jumping dog"
  10. }

The API returns the following response. There is now only one dog token in position 1.

  1. {
  2.   "tokens": [
  3.     {
  4.       "token": "jumping",
  5.       "start_offset": 0,
  6.       "end_offset": 7,
  7.       "type": "word",
  8.       "position": 0
  9.     },
  10.     {
  11.       "token": "jump",
  12.       "start_offset": 0,
  13.       "end_offset": 7,
  14.       "type": "word",
  15.       "position": 0
  16.     },
  17.     {
  18.       "token": "dog",
  19.       "start_offset": 8,
  20.       "end_offset": 11,
  21.       "type": "word",
  22.       "position": 1
  23.     }
  24.   ]
  25. }

Add to an analyzer

The following create index API request uses the remove_duplicates filter to configure a new custom analyzer.

This custom analyzer uses the keyword_repeat and stemmer filters to create a stemmed and unstemmed version of each token in a stream. The remove_duplicates filter then removes any duplicate tokens in the same position.

  1. PUT my-index-000001
  2. {
  3.   "settings": {
  4.     "analysis": {
  5.       "analyzer": {
  6.         "my_custom_analyzer": {
  7.           "tokenizer": "standard",
  8.           "filter": [
  9.             "keyword_repeat",
  10.             "stemmer",
  11.             "remove_duplicates"
  12.           ]
  13.         }
  14.       }
  15.     }
  16.   }
  17. }