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The StopWordDictionary class is designed to store stop words in an index. Stop words are excluded from indexing only if the UseStopWords index setting is enabled. Information on using stop words during indexing is provided on the Indexing with stop words page.

Note

Stop words define which terms of documents are indexed. Therefore, the stop word dictionary and the UseStopWords setting of an index can be changed only while the index contains no documents and is not performing an operation; otherwise, a change throws InvalidOperationException. A call that does not change the content of the dictionary is allowed. Configure stop words after creating a new index and before adding documents. See also the Index format and compatibility page.

The dictionary keeps words in lower case without leading and trailing white space. Therefore, the letter case of words does not matter when words are added, removed or checked.

To get the number of stop words in the dictionary, use the Count property.

To add stop words to the dictionary, use the AddRange method.

To remove words from the dictionary, use the RemoveRange method.

To check for a word in the dictionary, use the Contains method. The method ignores the letter case of the word.

To remove all words from the dictionary, use the Clear method.

To export words to a file, use the ExportDictionary method.

To import words from a file, use the ImportDictionary method. Errors of exporting and importing are reported by the ErrorOccurred event of the index instead of exceptions.

The following example demonstrates the use of methods of the stop word dictionary.

C#

string indexFolder = @"c:\MyIndex\";
string documentsFolder = @"c:\MyDocuments\";

// Creating an index settings instance
IndexSettings settings = new IndexSettings();
settings.UseStopWords = true; // Enabling the use of stop words during indexing

// Creating a new index in the specified folder; the dictionary can be changed only while the index contains no documents
Index index = new Index(indexFolder, settings, true);

if (index.Dictionaries.StopWordDictionary.Count > 0)
{
    // Removing all words from the dictionary
    index.Dictionaries.StopWordDictionary.Clear();
}

// Adding stop words to the dictionary
string[] words = new string[] { "a", "an", "the", "but", "by" };
index.Dictionaries.StopWordDictionary.AddRange(words);

// The letter case of words is ignored
if (index.Dictionaries.StopWordDictionary.Contains("But") &&
    index.Dictionaries.StopWordDictionary.Contains("BY"))
{
    // Removing words from the dictionary
    index.Dictionaries.StopWordDictionary.RemoveRange(new string[] { "but", "by" });
}

// Exporting words to a file
index.Dictionaries.StopWordDictionary.ExportDictionary(@"c:\StopWords.txt");

// Importing words from a file
index.Dictionaries.StopWordDictionary.ImportDictionary(@"c:\StopWords.txt");

// Indexing documents; after that, the stop words of the index cannot be changed
index.Add(documentsFolder);

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