Elasticsearch Analysis 分析器

• Analysis —文字分析是把全文字轉換一系列單詞（term/token)的過程，也叫分詞
• Analysis是透過Analyzer來實現的
  • 可使用 Elasticsearch 內建的分析器/或者按需定製化分析器
  • 除了在資料寫入時轉換詞條，匹配Query語句時候也需要用相同的分析器對查詢語句進行分析

Analyzer 分析器組成

分詞器是專門處理分詞的元件，由三部分組成

• Character Filters(針對原始文字處理，例如去除HTML)
• Tokenizer 安裝規則分詞
• Token Filter 將切分的單詞進行加工、小寫，刪除stopwords，增加同義詞

使用 Analyzer 分析器進行分詞

analyzer 分析器:

• Simple Analyzer – 按照非字母切分（符號被過濾），小寫處理
• Stop Analyzer – 小寫處理，停用詞過濾（the，a，is）
• Whitespace Analyzer – 按照空格切分，不轉小寫
• Keyword Analyzer – 不分詞，直接將輸入當作輸出
• Patter Analyzer – 正規表示式，預設 W+ (非字元分隔)
• Language – 提供了30多種常見語言的分詞器

檢視不同 analyzer 分析器的效果

standard 標準分析器(預設)

GET _analyze
{
  "analyzer": "standard",
  "text": "2 running Quick brown-foxes leap over lazy dogs in the summer evening."
}

=================== 結果 V ===================
{
  "tokens" : [
    {
      "token" : "2",
      "start_offset" : 0,
      "end_offset" : 1,
      "type" : "",
      "position" : 0
    },
    {
      "token" : "running",
      "start_offset" : 2,
      "end_offset" : 9,
      "type" : "",
      "position" : 1
    },
    ......
    {
      "token" : "evening",
      "start_offset" : 62,
      "end_offset" : 69,
      "type" : "",
      "position" : 12
    }
  ]
}

GET _analyze
{
  "analyzer": "stop",
  "text": "2 running Quick brown-foxes leap over lazy dogs in the summer evening."
}

=================== 結果 V ===================
{
  "tokens" : [
    {
      "token" : "running",
      "start_offset" : 2,
      "end_offset" : 9,
      "type" : "word",
      "position" : 0
    },
    {
      "token" : "quick",
      "start_offset" : 10,
      "end_offset" : 15,
      "type" : "word",
      "position" : 1
    },
    ......
    {
      "token" : "evening",
      "start_offset" : 62,
      "end_offset" : 69,
      "type" : "word",
      "position" : 11
    }
  ]
}

更多分詞器例子

#simpe
GET _analyze
{
  "analyzer": "simple",
  "text": "2 running Quick brown-foxes leap over lazy dogs in the summer evening."
}


GET _analyze
{
  "analyzer": "stop",
  "text": "2 running Quick brown-foxes leap over lazy dogs in the summer evening."
}


#stop
GET _analyze
{
  "analyzer": "whitespace",
  "text": "2 running Quick brown-foxes leap over lazy dogs in the summer evening."
}

#keyword
GET _analyze
{
  "analyzer": "keyword",
  "text": "2 running Quick brown-foxes leap over lazy dogs in the summer evening."
}

GET _analyze
{
  "analyzer": "pattern",
  "text": "2 running Quick brown-foxes leap over lazy dogs in the summer evening."
}


#english
GET _analyze
{
  "analyzer": "english",
  "text": "2 running Quick brown-foxes leap over lazy dogs in the summer evening."
}


POST _analyze
{
  "analyzer": "icu_analyzer",
  "text": "他說的確實在理”"
}


POST _analyze
{
  "analyzer": "standard",
  "text": "他說的確實在理”"
}


POST _analyze
{
  "analyzer": "icu_analyzer",
  "text": "這個蘋果不大好吃"
}

需要注意的是, icu_analyzer 分析器; 包括 ik 分析器; 並非 Elasticsearch 7.8.0 自帶分析器.

需要執行命令:./bin/elasticsearch-plugin install analysis-icu 自行安裝並重啟 elasticsearch 才能使用

更多中文分詞

ik

支援自定義詞庫，支援熱更新分詞
gitee.com/mirrors/elasticsearch-analysis-ik?_from=gitee_search

THULAC

清華大學自然語言處理和社會人文計算實驗室的一套中文分詞器
gitee.com/puremilk/THULAC-Python?_from=gitee_search

相關閱讀

• www.elastic.co/guide/en/elasticsearch/reference/current/analyzer-anatomy.html