CODEWITHSUNDEEP
c#performancelistcompare
Tobi
Tobi

Reputation: 694

C# - Compare two List<T> Objects if keypairs are equal

I have got two List<T> objects. It is filled with objects of my own class iFile, which contains a file path and the last edited date from the last call of the program.
Now I want to compare these two Lists, but my current code is running quite too slow! (4min for ~70.000 entries)

Here's my code:

private static List<iFile> compareLists(List<iFile> old)
{
    List<iFile> cf = new List<iFile>();
    foreach(iFile file in files)
    {
        bool notChanged = false;

        iFile oldFile = files.Where(f => f.fPath == file.fPath).FirstOrDefault();
        if(oldFile != null & oldFile.lastChange.Equals(file.lastChange))
        {
            notChanged = true;
        }
        if(!notChanged)
        {
            cf.Add(file);
        }
    }
    return cf;
}

What would you suggest to change to get better performance results?

Upvotes: 1

Views: 81

Answers (1)

Sergey Berezovskiy
Sergey Berezovskiy

Reputation: 236228

You can join files by fPath. That will internally use hash set to find matches between two collections. Unlike simple Where search which has complexity O(N), search in hash set has O(1) complexity:

var modifiedFiles = from file in files
                    join oldFile in old on file.fPath equals oldFile.fPath
                    where oldFile.lastChange != file.lastChange
                    select file;

return modifiedFiles.ToList();

Upvotes: 1

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