Wildcard search

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

In text form of a search query, 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 groups of wildcard characters are less and closer to the end of a search query.

It is important to know that wildcard search is flexible enough to use for prefix queries, since prefix query is a special case of a wildcard query.

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 methods for adding known parts of a word and wildcards to a template. 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);

More resources

GitHub examples

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

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