Package 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, Unwrappable<TokenStream>
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.

  • Constructor Details

    • KoreanNumberFilter

      public KoreanNumberFilter(TokenStream input)

  • Method Details

    • 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