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Test an analyzer

The analyze API is an invaluable tool for viewing the terms produced by an analyzer. A built-in analyzer can be specified inline in the request:

POST _analyze
{
  "analyzer": "whitespace",
  "text":     "The quick brown fox."
}

The API returns the following response:

{
  "tokens": [
    {
      "token": "The",
      "start_offset": 0,
      "end_offset": 3,
      "type": "word",
      "position": 0
    },
    {
      "token": "quick",
      "start_offset": 4,
      "end_offset": 9,
      "type": "word",
      "position": 1
    },
    {
      "token": "brown",
      "start_offset": 10,
      "end_offset": 15,
      "type": "word",
      "position": 2
    },
    {
      "token": "fox.",
      "start_offset": 16,
      "end_offset": 20,
      "type": "word",
      "position": 3
    }
  ]
}

You can also test combinations of:

A tokenizer
Zero or more token filters
Zero or more character filters

POST _analyze
{
  "tokenizer": "standard",
  "filter":  [ "lowercase", "asciifolding" ],
  "text":      "Is this déja vu?"
}

The API returns the following response:

{
  "tokens": [
    {
      "token": "is",
      "start_offset": 0,
      "end_offset": 2,
      "type": "<ALPHANUM>",
      "position": 0
    },
    {
      "token": "this",
      "start_offset": 3,
      "end_offset": 7,
      "type": "<ALPHANUM>",
      "position": 1
    },
    {
      "token": "deja",
      "start_offset": 8,
      "end_offset": 12,
      "type": "<ALPHANUM>",
      "position": 2
    },
    {
      "token": "vu",
      "start_offset": 13,
      "end_offset": 15,
      "type": "<ALPHANUM>",
      "position": 3
    }
  ]
}

Alternatively, a custom analyzer can be referred to when running the analyze API on a specific index:

PUT my-index-000001
{
  "settings": {
    "analysis": {
      "analyzer": {
        "std_folded": { 
          "type": "custom",
          "tokenizer": "standard",
          "filter": [
            "lowercase",
            "asciifolding"
          ]
        }
      }
    }
  },
  "mappings": {
    "properties": {
      "my_text": {
        "type": "text",
        "analyzer": "std_folded" 
      }
    }
  }
}

GET my-index-000001/_analyze 
{
  "analyzer": "std_folded", 
  "text":     "Is this déjà vu?"
}

GET my-index-000001/_analyze 
{
  "field": "my_text", 
  "text":  "Is this déjà vu?"
}

The API returns the following response:

{
  "tokens": [
    {
      "token": "is",
      "start_offset": 0,
      "end_offset": 2,
      "type": "<ALPHANUM>",
      "position": 0
    },
    {
      "token": "this",
      "start_offset": 3,
      "end_offset": 7,
      "type": "<ALPHANUM>",
      "position": 1
    },
    {
      "token": "deja",
      "start_offset": 8,
      "end_offset": 12,
      "type": "<ALPHANUM>",
      "position": 2
    },
    {
      "token": "vu",
      "start_offset": 13,
      "end_offset": 15,
      "type": "<ALPHANUM>",
      "position": 3
    }
  ]
}

	Define a `custom` analyzer called `std_folded`.
	The field `my_text` uses the `std_folded` analyzer.
	To refer to this analyzer, the `analyze` API must specify the index name.
	Refer to the analyzer by name.
	Refer to the analyzer used by field `my_text`.

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https://www.elastic.co/guide/en/elasticsearch/reference/7.17/test-analyzer.html