How to: Compare the Contents of Two Folders (LINQ)

This example demonstrates three ways to compare two file listings:

·         By querying for a Boolean value that specifies whether the two file lists are identical.

·         By querying for the intersection to retrieve the files that are in both folders.

·         By querying for the set difference to retrieve the files that are in one folder but not the other.

Note:

The techniques shown here can be adapted to compare sequences of objects of any type.

The FileComparer class shown here demonstrates how to use a custom comparer class together with the Standard Query Operators. The class is not intended for use in real-world scenarios. It just uses the name and length in bytes of each file to determine whether the contents of each folder are identical or not. In a real-world scenario, you should modify this comparer to perform a more rigorous equality check.

 Example

Visual Basic

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Module CompareDirs

    Public Sub Main()

        ' Create two identical or different temporary folders 

        ' on a local drive and add files to them.

        ' Then set these file paths accordingly.

        Dim pathA As String = "C:\TestDir"

        Dim pathB As String = "C:\TestDir2"

        ' Take a snapshot of the file system.

        Dim list1 = GetFiles(pathA)

        Dim list2 = GetFiles(pathB)

        ' Create the FileCompare object we'll use in each query

        Dim myFileCompare As New FileCompare

        ' This query determines whether the two folders contain

        ' identical file lists, based on the custom file comparer

        ' that is defined in the FileCompare class.

        ' The query executes immediately because it returns a bool.

        Dim areIdentical As Boolean = list1.SequenceEqual(list2, myFileCompare)

        If areIdentical = True Then

            Console.WriteLine("The two folders are the same.")

        Else

            Console.WriteLine("The two folders are not the same.")

        End If

        ' Find common files in both folders. It produces a sequence and doesn't execute

        ' until the foreach statement.

        Dim queryCommonFiles = list1.Intersect(list2, myFileCompare)

        If queryCommonFiles.Count() > 0 Then

            Console.WriteLine("The following files are in both folders:")

            For Each fi As System.IO.FileInfo In queryCommonFiles

                Console.WriteLine(fi.FullName)

            Next

        Else

            Console.WriteLine("There are no common files in the two folders.")

        End If

        ' Find the set difference between the two folders.

        ' For this example we only check one way.

        Dim queryDirAOnly = list1.Except(list2, myFileCompare)

        Console.WriteLine("The following files are in dirA but not dirB:")

        For Each fi As System.IO.FileInfo In queryDirAOnly

            Console.WriteLine(fi.FullName)

        Next

        ' Keep the console window open in debug mode

        Console.WriteLine("Press any key to exit.")

        Console.ReadKey()

    End Sub

    ' This implementation defines a very simple comparison

    ' between two FileInfo objects. It only compares the name

    ' of the files being compared and their length in bytes.

    Public Class FileCompare

        Implements System.Collections.Generic.IEqualityComparer(Of System.IO.FileInfo)

        Public Function Equals1(ByVal x As System.IO.FileInfo, ByVal y As System.IO.FileInfo) _

            As Boolean Implements System.Collections.Generic.IEqualityComparer(Of System.IO.FileInfo).Equals

            If (x.Name = y.Name) And (x.Length = y.Length) Then

                Return True

            Else

                Return False

            End If

        End Function

        ' Return a hash that reflects the comparison criteria. According to the 

        ' rules for IEqualityComparer(Of T), if Equals is true, then the hash codes must

        ' also be equal. Because equality as defined here is a simple value equality, not

        ' reference identity, it is possible that two or more objects will produce the same

        ' hash code.

        Public Function GetHashCode1(ByVal fi As System.IO.FileInfo) _

            As Integer Implements System.Collections.Generic.IEqualityComparer(Of System.IO.FileInfo).GetHashCode

            Dim s As String = fi.Name & fi.Length

            Return s.GetHashCode()

        End Function

    End Class

    ' Function to retrieve a list of files. Note that this is a copy

    ' of the file information.

    Function GetFiles(ByVal root As String) As IEnumerable(Of System.IO.FileInfo)

        Return From file In My.Computer.FileSystem.GetFiles _

                  (root, FileIO.SearchOption.SearchAllSubDirectories, "*.*") _

               Select New System.IO.FileInfo(file)

    End Function

End Module

C#

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namespace QueryCompareTwoDirs

{

    class CompareDirs

    {

        static void Main(string[] args)

        {

            // Create two identical or different temporary folders 

            // on a local drive and change these file paths.

            string pathA = @"C:\TestDir";

            string pathB = @"C:\TestDir2";

            // Take a snapshot of the file system.

            IEnumerable<System.IO.FileInfo> list1 = GetFiles(pathA);

            IEnumerable<System.IO.FileInfo> list2 = GetFiles(pathB);

            //A custom file comparer defined below

            FileCompare myFileCompare = new FileCompare();

            // This query determines whether the two folders contain

            // identical file lists, based on the custom file comparer

            // that is defined in the FileCompare class.

            // The query executes immediately because it returns a bool.

            bool areIdentical = list1.SequenceEqual(list2, myFileCompare);

            if (areIdentical == true)

            {

                Console.WriteLine("the two folders are the same");

            }

            else

            {

                Console.WriteLine("The two folders are not the same");

            }

            // Find the common files. It produces a sequence and doesn't 

            // execute until the foreach statement.

            var queryCommonFiles = list1.Intersect(list2, myFileCompare);

            if (queryCommonFiles.Count() > 0)

            {

                Console.WriteLine("The following files are in both folders:");

                foreach (var v in queryCommonFiles)

                {

                    Console.WriteLine(v.FullName); //shows which items end up in result list

                }

            }

            else

            {

                Console.WriteLine("There are no common files in the two folders.");

            }

            // Find the set difference between the two folders.

            // For this example we only check one way.

            var queryList1Only = (from file in list1

                                  select file).Except(list2, myFileCompare);

            Console.WriteLine("The following files are in list1 but not list2:");

            foreach (var v in queryList1Only)

            {

                Console.WriteLine(v.FullName);

            }

            // Keep the console window open in debug mode.

            Console.WriteLine("Press any key to exit.");

            Console.ReadKey();

        }            

        // This method assumes that the application has discovery 

        // permissions for all folders under the specified path.

        static IEnumerable<System.IO.FileInfo> GetFiles(string path)

        {

            if (!System.IO.Directory.Exists(path))

                throw new System.IO.DirectoryNotFoundException();

            string[] fileNames = null;

            List<System.IO.FileInfo> files = new List<System.IO.FileInfo>();

            fileNames = System.IO.Directory.GetFiles(path, "*.*", System.IO.SearchOption.AllDirectories);            

            foreach (string name in fileNames)

            {

                files.Add(new System.IO.FileInfo(name));

            }

            return files;

        }

    }

    // This implementation defines a very simple comparison

    // between two FileInfo objects. It only compares the name

    // of the files being compared and their length in bytes.

    class FileCompare : System.Collections.Generic.IEqualityComparer<System.IO.FileInfo>

    {

        public FileCompare() { }

        public bool Equals(System.IO.FileInfo f1, System.IO.FileInfo f2)

        {

            return (f1.Name == f2.Name &&

                    f1.Length == f2.Length);

        }

        // Return a hash that reflects the comparison criteria. According to the 

        // rules for IEqualityComparer<T>, if Equals is true, then the hash codes must

        // also be equal. Because equality as defined here is a simple value equality, not

        // reference identity, it is possible that two or more objects will produce the same

        // hash code.

        public int GetHashCode(System.IO.FileInfo fi)

        {

            string s = String.Format("{0}{1}", fi.Name, fi.Length);

            return s.GetHashCode();

        }

    }

}

 Compiling the Code

·         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 the code into your project.

·         Press F5 to compile and run the program.

·         Press any key to exit the console window.

 Robust Programming

For intensive query operations over the contents of multiple types of documents and files, consider using the Windows Desktop Search engine.

 See Also

Concepts

LINQ to Objects

LINQ and File Directories