org.apache.lucene.analysis.ko

## Class KoreanNumberFilter

- java.lang.Object
- - org.apache.lucene.util.AttributeSource
  - - org.apache.lucene.analysis.TokenStream
    - - org.apache.lucene.analysis.TokenFilter
      - - org.apache.lucene.analysis.ko.KoreanNumberFilter

- All Implemented Interfaces:
    Closeable, AutoCloseable

      public class KoreanNumberFilter
      extends TokenFilter

  A `TokenFilter` that normalizes Korean numbers to regular Arabic decimal numbers in half-width characters.

  Korean numbers are often written using a combination of Hangul and Arabic numbers with various kinds punctuation. For example, ３．２천 means 3200. This filter does this kind of normalization and allows a search for 3200 to match ３．２천 in text, but can also be used to make range facets based on the normalized numbers and so on.

  Notice that this analyzer uses a token composition scheme and relies on punctuation tokens being found in the token stream. Please make sure your `KoreanTokenizer` has `discardPunctuation` set to false. In case punctuation characters, such as ． (U+FF0E FULLWIDTH FULL STOP), is removed from the token stream, this filter would find input tokens tokens ３ and ２천 and give outputs 3 and 2000 instead of 3200, which is likely not the intended result. If you want to remove punctuation characters from your index that are not part of normalized numbers, add a `StopFilter` with the punctuation you wish to remove after `KoreanNumberFilter` in your analyzer chain.

  Below are some examples of normalizations this filter supports. The input is untokenized text and the result is the single term attribute emitted for the input.

  - 영영칠 becomes 7
  - 일영영영 becomes 1000
  - 삼천2백2십삼 becomes 3223
  - 조육백만오천일 becomes 1000006005001
  - ３.２천 becomes 3200
  - １.２만３４５.６７ becomes 12345.67
  - 4,647.100 becomes 4647.1
  - 15,7 becomes 157 (be aware of this weakness)

  Tokens preceded by a token with `PositionIncrementAttribute` of zero are left left untouched and emitted as-is.

  This filter does not use any part-of-speech information for its normalization and the motivation for this is to also support n-grammed token streams in the future.

  This filter may in some cases normalize tokens that are not numbers in their context. For example, is 전중경일 is a name and means Tanaka Kyōichi, but 경일 (Kyōichi) out of context can strictly speaking also represent the number 10000000000000001. This filter respects the `KeywordAttribute`, which can be used to prevent specific normalizations from happening.

  WARNING: This API is experimental and might change in incompatible ways in the next release.

- - ### Nested Class Summary

    Nested Classes
    Modifier and Type | Class and Description
    --- | ---
    `static class` | `KoreanNumberFilter.NumberBuffer` Buffer that holds a Korean number string and a position index used as a parsed-to marker

    - ### Nested classes/interfaces inherited from class org.apache.lucene.util.AttributeSource

      `AttributeSource.State`

  - ### Field Summary

    - ### Fields inherited from class org.apache.lucene.analysis.TokenFilter

      `input`

    - ### Fields inherited from class org.apache.lucene.analysis.TokenStream

      `DEFAULT_TOKEN_ATTRIBUTE_FACTORY`

  - ### Constructor Summary

    Constructors
    Constructor and Description
    `KoreanNumberFilter(TokenStream input)`

  - ### Method Summary

    All Methods Instance Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `boolean` | `incrementToken()`
    `boolean` | `isArabicNumeral(char c)` Arabic numeral predicate.
    `boolean` | `isNumeral(char c)` Numeral predicate
    `boolean` | `isNumeral(String input)` Numeral predicate
    `boolean` | `isNumeralPunctuation(char c)` Numeral punctuation predicate
    `boolean` | `isNumeralPunctuation(String input)` Numeral punctuation predicate
    `String` | `normalizeNumber(String number)` Normalizes a Korean number
    `BigDecimal` | `parseLargeHangulNumeral(KoreanNumberFilter.NumberBuffer buffer)` Parse large Hangul numerals (ten thousands or larger)
    `BigDecimal` | `parseMediumHangulNumeral(KoreanNumberFilter.NumberBuffer buffer)` Parse medium Hangul numerals (tens, hundreds or thousands)
    `void` | `reset()`

    - ### Methods inherited from class org.apache.lucene.analysis.TokenFilter

      `close, end`

    - ### Methods inherited from class org.apache.lucene.util.AttributeSource

      `addAttribute, addAttributeImpl, captureState, clearAttributes, cloneAttributes, copyTo, endAttributes, equals, getAttribute, getAttributeClassesIterator, getAttributeFactory, getAttributeImplsIterator, hasAttribute, hasAttributes, hashCode, reflectAsString, reflectWith, removeAllAttributes, restoreState, toString`

    - ### Methods inherited from class java.lang.Object

      `clone, finalize, getClass, notify, notifyAll, wait, wait, wait`

- - ### Constructor Detail

    - #### KoreanNumberFilter

          public KoreanNumberFilter(TokenStream input)

  - ### Method Detail

    - #### incrementToken

          public final boolean incrementToken()
                                       throws IOException

      Specified by:
        `incrementToken` in class `TokenStream`
      Throws:
        `IOException`

    - #### reset

          public void reset()
                     throws IOException

      Overrides:
        `reset` in class `TokenFilter`
      Throws:
        `IOException`

    - #### normalizeNumber

          public String normalizeNumber(String number)

      Normalizes a Korean number
      Parameters:
        `number` - number or normalize
      Returns:
        normalized number, or number to normalize on error (no op)

    - #### parseLargeHangulNumeral

          public BigDecimal parseLargeHangulNumeral(KoreanNumberFilter.NumberBuffer buffer)

      Parse large Hangul numerals (ten thousands or larger)
      Parameters:
        `buffer` - buffer to parse
      Returns:
        parsed number, or null on error or end of input

    - #### parseMediumHangulNumeral

          public BigDecimal parseMediumHangulNumeral(KoreanNumberFilter.NumberBuffer buffer)

      Parse medium Hangul numerals (tens, hundreds or thousands)
      Parameters:
        `buffer` - buffer to parse
      Returns:
        parsed number or null on error

    - #### isNumeral

          public boolean isNumeral(String input)

      Numeral predicate
      Parameters:
        `input` - string to test
      Returns:
        true if and only if input is a numeral

    - #### isNumeral

          public boolean isNumeral(char c)

      Numeral predicate
      Parameters:
        `c` - character to test
      Returns:
        true if and only if c is a numeral

    - #### isNumeralPunctuation

          public boolean isNumeralPunctuation(String input)

      Numeral punctuation predicate
      Parameters:
        `input` - string to test
      Returns:
        true if and only if c is a numeral punctuation string

    - #### isNumeralPunctuation

          public boolean isNumeralPunctuation(char c)

      Numeral punctuation predicate
      Parameters:
        `c` - character to test
      Returns:
        true if and only if c is a numeral punctuation character

    - #### isArabicNumeral

          public boolean isArabicNumeral(char c)

      Arabic numeral predicate. Both half-width and full-width characters are supported
      Parameters:
        `c` - character to test
      Returns:
        true if and only if c is an Arabic numeral

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