Czech analyzer

The built-in czech analyzer can be applied to a text field using the following command:

  1. PUT /czech-index
  2. {
  3.   "mappings": {
  4.     "properties": {
  5.       "content": {
  6.         "type": "text",
  7.         "analyzer": "czech"
  8.       }
  9.     }
  10.   }
  11. }

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Stem exclusion

You can use stem_exclusion with this language analyzer using the following command:

  1. PUT index_with_stem_exclusion_czech_analyzer
  2. {
  3.   "settings": {
  4.     "analysis": {
  5.       "analyzer": {
  6.         "stem_exclusion_czech_analyzer": {
  7.           "type": "czech",
  8.           "stem_exclusion": ["autorita", "schválení"]
  9.         }
  10.       }
  11.     }
  12.   }
  13. }

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Czech analyzer internals

The czech analyzer is built using the following components:

  • Tokenizer: standard

  • Token filters:

    • lowercase
    • stop (Czech)
    • keyword
    • stemmer (Czech)

Custom Czech analyzer

You can create a custom Czech analyzer using the following command:

  1. PUT /czech-index
  2. {
  3.   "settings": {
  4.     "analysis": {
  5.       "filter": {
  6.         "czech_stop": {
  7.           "type": "stop",
  8.           "stopwords": "_czech_"
  9.         },
  10.         "czech_stemmer": {
  11.           "type": "stemmer",
  12.           "language": "czech"
  13.         },
  14.         "czech_keywords": {
  15.           "type":       "keyword_marker",
  16.           "keywords":   [] 
  17.         }
  18.       },
  19.       "analyzer": {
  20.         "czech_analyzer": {
  21.           "type": "custom",
  22.           "tokenizer": "standard",
  23.           "filter": [
  24.             "lowercase",
  25.             "czech_stop",
  26.             "czech_keywords",
  27.             "czech_stemmer"
  28.           ]
  29.         }
  30.       }
  31.     }
  32.   },
  33.   "mappings": {
  34.     "properties": {
  35.       "content": {
  36.         "type": "text",
  37.         "analyzer": "czech_analyzer"
  38.       }
  39.     }
  40.   }
  41. }

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Generated tokens

Use the following request to examine the tokens generated using the analyzer:

  1. POST /czech-index/_analyze
  2. {
  3.   "field": "content",
  4.   "text": "Studenti studují na českých univerzitách. Jejich čísla jsou 123456."
  5. }

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The response contains the generated tokens:

  1. {
  2.   "tokens": [
  3.     {
  4.       "token": "student",
  5.       "start_offset": 0,
  6.       "end_offset": 8,
  7.       "type": "<ALPHANUM>",
  8.       "position": 0
  9.     },
  10.     {
  11.       "token": "studuj",
  12.       "start_offset": 9,
  13.       "end_offset": 16,
  14.       "type": "<ALPHANUM>",
  15.       "position": 1
  16.     },
  17.     {
  18.       "token": "česk",
  19.       "start_offset": 20,
  20.       "end_offset": 27,
  21.       "type": "<ALPHANUM>",
  22.       "position": 3
  23.     },
  24.     {
  25.       "token": "univerzit",
  26.       "start_offset": 28,
  27.       "end_offset": 40,
  28.       "type": "<ALPHANUM>",
  29.       "position": 4
  30.     },
  31.     {
  32.       "token": "čísl",
  33.       "start_offset": 49,
  34.       "end_offset": 54,
  35.       "type": "<ALPHANUM>",
  36.       "position": 6
  37.     },
  38.     {
  39.       "token": "123456",
  40.       "start_offset": 60,
  41.       "end_offset": 66,
  42.       "type": "<NUM>",
  43.       "position": 8
  44.     }
  45.   ]
  46. }