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How to: Count Occurrences of a Word in a String (LINQ) (Visual Basic)

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This example shows how to use a LINQ query to count the occurrences of a specified word in a string. Note that to perform the count, first the Split method is called to create an array of words. There is a performance cost to the Split method. If the only operation on the string is to count the words, you should consider using the Matches or IndexOf methods instead. However, if performance is not a critical issue, or you have already split the sentence in order to perform other types of queries over it, then it makes sense to use LINQ to count the words or phrases as well.

Example

Class CountWords

    Shared Sub Main()

        Dim text As String = "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."

        Dim searchTerm As String = "data"

        ' Convert the string into an array of words.
        Dim dataSource As String() = text.Split(New Char() {" ", ",", ".", ";", ":"},
                                                 StringSplitOptions.RemoveEmptyEntries)

        ' Create and execute the query. It executes immediately
        ' because a singleton value is produced.
        ' Use ToLower to match "data" and "Data"
        Dim matchQuery = From word In dataSource
                      Where word.ToLowerInvariant() = searchTerm.ToLowerInvariant()
                      Select word

        ' Count the matches.
        Dim count As Integer = matchQuery.Count()
        Console.WriteLine(count & " occurrence(s) of the search term """ &
                          searchTerm & """ were found.")

        ' Keep console window open in debug mode.
        Console.WriteLine("Press any key to exit.")
        Console.ReadKey()
    End Sub
End Class
' Output:
' 3 occurrence(s) of the search term "data" were found.

Compile the code

Create a Visual Basic console application project, with an Imports statement for the System.Linq namespace.

See also