Class ASCIIFoldingFilter

This class converts alphabetic, numeric, and symbolic Unicode characters which are not in the first 127 ASCII characters (the "Basic Latin" Unicode block) into their ASCII equivalents, if one exists.

Characters from the following Unicode blocks are converted; however, only those characters with reasonable ASCII alternatives are converted:

See: http://en.wikipedia.org/wiki/Latin_characters_in_Unicode

For example, 'à' will be replaced by 'a'.
Inheritance
object
AttributeSource
TokenStream
TokenFilter
ASCIIFoldingFilter
Implements
Inherited Members
TokenFilter.End()
TokenStream.Dispose()
AttributeSource.GetAttributeFactory()
AttributeSource.GetAttributeClassesEnumerator()
AttributeSource.GetAttributeImplsEnumerator()
AttributeSource.AddAttributeImpl(Attribute)
AttributeSource.AddAttribute<T>()
AttributeSource.HasAttributes
AttributeSource.HasAttribute<T>()
AttributeSource.GetAttribute<T>()
AttributeSource.ClearAttributes()
AttributeSource.CaptureState()
AttributeSource.RestoreState(AttributeSource.State)
AttributeSource.GetHashCode()
AttributeSource.ReflectWith(IAttributeReflector)
AttributeSource.CloneAttributes()
AttributeSource.CopyTo(AttributeSource)
AttributeSource.ToString()
Namespace: Lucene.Net.Analysis.Miscellaneous
Assembly: Lucene.Net.Analysis.Common.dll
Syntax
public sealed class ASCIIFoldingFilter : TokenFilter, IDisposable

Constructors

ASCIIFoldingFilter(TokenStream)

This class converts alphabetic, numeric, and symbolic Unicode characters which are not in the first 127 ASCII characters (the "Basic Latin" Unicode block) into their ASCII equivalents, if one exists.

Characters from the following Unicode blocks are converted; however, only those characters with reasonable ASCII alternatives are converted:

See: http://en.wikipedia.org/wiki/Latin_characters_in_Unicode

For example, '&agrave;' will be replaced by 'a'.
Declaration
public ASCIIFoldingFilter(TokenStream input)
Parameters
Type Name Description
TokenStream input

ASCIIFoldingFilter(TokenStream, bool)

Create a new ASCIIFoldingFilter.

Declaration
public ASCIIFoldingFilter(TokenStream input, bool preserveOriginal)
Parameters
Type Name Description
TokenStream input

TokenStream to filter
bool preserveOriginal

should the original tokens be kept on the input stream with a 0 position increment from the folded tokens?

Properties

PreserveOriginal

Does the filter preserve the original tokens?

Declaration
public bool PreserveOriginal { get; }
Property Value
Type Description
bool

Methods

FoldToASCII(char[], int)

Converts characters above ASCII to their ASCII equivalents. For example, accents are removed from accented characters.

Declaration
public void FoldToASCII(char[] input, int length)
Parameters
Type Name Description
char[] input

The string to fold
int length

The number of characters in the input string

FoldToASCII(char[], int, char[], int, int)

Converts characters above ASCII to their ASCII equivalents. For example, accents are removed from accented characters.

Note

This API is for internal purposes only and might change in incompatible ways in the next release.

Declaration
public static int FoldToASCII(char[] input, int inputPos, char[] output, int outputPos, int length)
Parameters
Type Name Description
char[] input

The characters to fold
int inputPos

Index of the first character to fold
char[] output

The result of the folding. Should be of size >= length * 4.
int outputPos

Index of output where to put the result of the folding
int length

The number of characters to fold
Returns
Type Description
int

length of output

IncrementToken()

Consumers (i.e., Lucene.Net.Index.IndexWriter) use this method to advance the stream to the next token. Implementing classes must implement this method and update the appropriate Lucene.Net.Util.IAttributes with the attributes of the next token.

The producer must make no assumptions about the attributes after the method has been returned: the caller may arbitrarily change it. If the producer needs to preserve the state for subsequent calls, it can use Lucene.Net.Util.AttributeSource.CaptureState() to create a copy of the current attribute state.

this method is called for every token of a document, so an efficient implementation is crucial for good performance. To avoid calls to Lucene.Net.Util.AttributeSource.AddAttribute<T>() and Lucene.Net.Util.AttributeSource.GetAttribute<T>(), references to all Lucene.Net.Util.IAttributes that this stream uses should be retrieved during instantiation.

To ensure that filters and consumers know which attributes are available, the attributes must be added during instantiation. Filters and consumers are not required to check for availability of attributes in Lucene.Net.Analysis.TokenStream.IncrementToken().
Declaration
public override bool IncrementToken()
Returns
Type Description
bool

false for end of stream; true otherwise
Overrides
Lucene.Net.Analysis.TokenStream.IncrementToken()

Reset()

This method is called by a consumer before it begins consumption using Lucene.Net.Analysis.TokenStream.IncrementToken().

Resets this stream to a clean state. Stateful implementations must implement this method so that they can be reused, just as if they had been created fresh.

If you override this method, always call base.Reset(), otherwise some internal state will not be correctly reset (e.g., Lucene.Net.Analysis.Tokenizer will throw InvalidOperationException on further usage).
Declaration
public override void Reset()
Overrides
Lucene.Net.Analysis.TokenFilter.Reset()
Remarks

NOTE: The default implementation chains the call to the input Lucene.Net.Analysis.TokenStream, so be sure to call base.Reset() when overriding this method.

Implements