Wildcard search Leave feedback

Wildcard search allows you to search for words with unknown letters or ranges of letters.

In a search query in text form, there are 2 forms of wildcard characters:

• ? for a single character;
• ?(n~m) for a group of characters, where n and m are numbers from 0 to 255, and n <= m.

Wildcard search is similar to regular expression search, but it works significantly faster when there are fewer groups of wildcard characters and they are closer to the end of a search query.

Wildcard search is flexible enough to be used for prefix queries, since a prefix query is a special case of a wildcard query. Since version 26.10, wildcard search uses as many threads as there are processor cores by default.

Examples of wildcard search with queries in text form are presented below.

C#

string indexFolder = @"c:\MyIndex\";
string documentsFolder = @"c:\MyDocuments\";
 
// Creating an index in the specified folder
Index index = new Index(indexFolder);
 
// Indexing documents from the specified folder
index.Add(documentsFolder);
 
// Search in the index
SearchResult result1 = index.Search("m?rry"); // Search for 'merry', 'marry', etc.
SearchResult result2 = index.Search("card?(1~6)"); // Search for 'cardiff', 'cardinal', 'cardio', 'cards', etc.

To build a query for the wildcard search in object form, use the WordPattern class. This class contains the following methods for adding known parts of a word and wildcards to a pattern:

• AppendString appends a string of known characters.
• AppendCharacter appends a known character.
• AppendOneCharacterWildcard appends a wildcard for exactly one character (? in text form).
• AppendZeroOrOneCharacterWildcard appends a wildcard for zero or one character (?(0~1) in text form).
• AppendZeroOrMoreCharactersWildcard appends a wildcard for zero to 255 characters (?(0~255) in text form).
• AppendOneOrMoreCharactersWildcard appends a wildcard for one to 255 characters (?(1~255) in text form).
• AppendWildcard appends a wildcard for the specified minimum and maximum numbers of characters (?(min~max) in text form). Both values must be in the range from 0 to 255, and the minimum must not be greater than the maximum; otherwise, ArgumentOutOfRangeException is thrown.

The known characters are converted to lower case, since words are stored in the index in lower case. An example of constructing a query in object form is presented below.

C#

string indexFolder = @"c:\MyIndex\";
string documentsFolder = @"c:\MyDocuments\";
 
// Creating an index in the specified folder
Index index = new Index(indexFolder);
 
// Indexing documents from the specified folder
index.Add(documentsFolder);
 
// Search with pattern "m?rry"
// Search for 'merry', 'marry', etc.
WordPattern pattern1 = new WordPattern();
pattern1.AppendString("m");
pattern1.AppendOneCharacterWildcard();
pattern1.AppendString("rry");
SearchQuery query1 = SearchQuery.CreateWordPatternQuery(pattern1);
SearchResult result1 = index.Search(query1);
 
// Search with pattern "card?(1~6)"
// Search for 'cardiff', 'cardinal', 'cardio', 'cards', etc.
WordPattern pattern2 = new WordPattern();
pattern2.AppendString("card");
pattern2.AppendWildcard(1, 6);
SearchQuery query2 = SearchQuery.CreateWordPatternQuery(pattern2);
SearchResult result2 = index.Search(query2);

You may easily run the code from documentation articles and see the features in action in our GitHub examples:

• GroupDocs.Search for .NET examples

• GroupDocs.Search for Java examples

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