Intersect method in LINQ with C#

Question

I am trying to obtain the same files using Intersect method from two folders. 123.xml files are the same (no change with content, date, size) in all the folders.

Scores\Content\123.xml
Scores\Content\hi.xml
Scores\123.xml

Power\Content\123.xml
Power\Content\helo.xml
Power\123.xml

This is from the C# code

        System.IO.DirectoryInfo dir1 = new System.IO.DirectoryInfo(path1);
        System.IO.DirectoryInfo dir2 = new System.IO.DirectoryInfo(path2);

        IEnumerable<System.IO.FileInfo> list1 = dir1.GetFiles("*.*", System.IO.SearchOption.AllDirectories);
        IEnumerable<System.IO.FileInfo> list2 = dir2.GetFiles("*.*", System.IO.SearchOption.AllDirectories);

        FileCompare myFileCompare = new FileCompare();

        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");
        }


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

The queryCommonFiles is only returning the 123.xml from Content folder, but not the other one.

This is the code from the FileCompare

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();
    }

}

EDIT:

var queryList1Only = (from file in list1
                                  select file).Except(list2, myFileCompare);

            Console.WriteLine("The following files are in list1 but not list2:\n");
            foreach (var v in queryList1Only)
            {
                Console.WriteLine(v.FullName);
            }


            var queryList2Only = (from file in list2
                                  select file).Except(list1, myFileCompare);

            Console.WriteLine("The following files are in list2 but not list1:\n");
            foreach (var v in queryList2Only)
            {
                Console.WriteLine(v.FullName);
            }

This produces as hi.xml for list1 and helo.xml for list2. And as I said only one 123.xml for the intersect method.

Any suggestions would be appreciated

Thanks,

Is it because "list1.Intersect" is actually comparing just the file names rather than the file names with folder structure ? — superstar, Jun 28 '11 at 18:23
I suggest you put some diagnostics into the Equals and GetHashCode methods... I expect the other files have different lengths, or something like that. — Jon Skeet, Jun 28 '11 at 18:25
@superstar the Name atribute in FileInfo does not have the path — Adriano Carneiro, Jun 28 '11 at 18:27
@Adrian: I saw that, I cannot use FullName there, since the folder structure for both the Scores and Power differs. — superstar, Jun 28 '11 at 18:30
If I have different lenghts or any difference in the two 123.xml files, I should get them in the comparison (under the EDIT), but I am getting only hi.xml in list1 and helo.xml for list2 as the differences — superstar, Jun 28 '11 at 18:33

score 3 · Accepted Answer · answered Jun 28 '11 at 18:54

I just changed the Equals method to achieve the desired results

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.Directory.Name == f2.Directory.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();
        }

    }

score 2 · Answer 2 · answered Jun 28 '11 at 18:24

2

Everything looks OK. Make sure both Scores\123.xml and Power\123.xml have the same length.

answered Jun 28 '11 at 18:24

Adriano Carneiro

57,693
12
90
123

They do have the same length, date and content. (I just copied the same file to both the folders) – superstar Jun 28 '11 at 18:25

Alex Peck · Answer 3 · 2011-06-28T19:06:03.207

2

Because you only compare using FileInfo.Name and FileInfo.Length, Content\123.xml is the same as 123.xml (assuming both files have the same size, which I'm guessing is the case for your test data).

Therefore, as far as your FileCompare class is concerned, your input collections contain duplicates. According to MSDN, Intersect evaluates distinct elements in each set.

edited Jun 28 '11 at 19:06

answered Jun 28 '11 at 18:52

Alex Peck

4,603
1
33
37

Yes, Intersect evaluates distinct elements. – superstar Jun 28 '11 at 18:53
Therefore, distinct elements of [123.xml, hi.xml, 123.xml] and [123.xml, helo.xml, 123.xml] are [123.xml, hi.xml] and [123.xml, helo.xml]. The intersection of these is the single element 123.xml. – Alex Peck Jun 28 '11 at 18:57
But I needed same files to be identified, so I modified the Equals method to handle it. – superstar Jun 28 '11 at 18:58

Intersect method in LINQ with C#

3 Answers3