How to: Query for Sentences that Contain a Specified Set of Words (LINQ)

This example shows how to find sentences in a text file that contain matches for each of a specified set of words. Although the array of search terms is hard-coded in this example, it could also be populated dynamically at runtime. In this example, the query returns the sentences that contain the words "Historically," "data," and "integrated."

class FindSentences
{
    static void Main()
    {
        string text = @"Historically, the world of data and the world of objects " +
        @"have not been well integrated. Programmers work in C# or Visual Basic " +
        @"and also in SQL or XQuery. On the one side are concepts such as classes, " +
        @"objects, fields, inheritance, and .NET Framework APIs. On the other side " +
        @"are tables, columns, rows, nodes, and separate languages for dealing with " +
        @"them. Data types often require translation between the two worlds; there are " +
        @"different standard functions. Because the object world has no notion of query, a " +
        @"query can only be represented as a string without compile-time type checking or " +
        @"IntelliSense support in the IDE. Transferring data from SQL tables or XML trees to " +
        @"objects in memory is often tedious and error-prone.";

        // Split the text block into an array of sentences. 
        string[] sentences = text.Split(new char[] { '.', '?', '!' });

        // Define the search terms. This list could also be dynamically populated at runtime. 
        string[] wordsToMatch = { "Historically", "data", "integrated" };

        // Find sentences that contain all the terms in the wordsToMatch array. 
        // Note that the number of terms to match is not specified at compile time. 
        var sentenceQuery = from sentence in sentences
                            let w = sentence.Split(new char[] { '.', '?', '!', ' ', ';', ':', ',' },
                                                    StringSplitOptions.RemoveEmptyEntries)
                            where w.Distinct().Intersect(wordsToMatch).Count() == wordsToMatch.Count()
                            select sentence;

        // Execute the query. Note that you can explicitly type 
        // the iteration variable here even though sentenceQuery 
        // was implicitly typed.  
        foreach (string str in sentenceQuery)
        {
            Console.WriteLine(str);
        }

        // Keep the console window open in debug mode.
        Console.WriteLine("Press any key to exit");
        Console.ReadKey();
    }
}
/* Output:
Historically, the world of data and the world of objects have not been well integrated
*/

The query works by first splitting the text into sentences, and then splitting the sentences into an array of strings that hold each word. For each of these arrays, the Distinct method removes all duplicate words, and then the query performs an Intersect operation on the word array and the wordstoMatch array. If the count of the intersection is the same as the count of the wordsToMatch array, all words were found in the words and the original sentence is returned.

In the call to Split, the punctuation marks are used as separators in order to remove them from the string. If you did not do this, for example you could have a string "Historically," that would not match "Historically" in the wordsToMatch array. You may have to use additional separators, depending on the types of punctuation found in the source text.

  • Create a Visual Studio project that targets the .NET Framework version 3.5. By default, the project has a reference to System.Core.dll and a using directive (C#) or Imports statement (Visual Basic) for the System.Linq namespace. In C# projects, add a using directive for the System.IO namespace.

  • Copy this code into your project.

  • Press F5 to compile and run the program.

  • Press any key to exit the console window.

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