Sorting files with the same first 3 letters, than deleting the older files?

I had a question last week, and you quickly alleviated any concern that it wo开发者_Python百科uld roadblock me, hoping that you can help a beginner program once more!

I'm trying to automate one of my daily mundane tasks and it's being quite a bugger, I think mainly because I'm not taking the correct approach.

Each morning I go through a system directory that houses many files with the same prefix, and a generated number following it. I have to sort alphabetically first, then remove the oldest versions of that file.

Here's an example pic of my directory: http://i.imgur.com/5l2Am.png

I was going to approach this situation by just sorting the files by name and comparing the first 3 letters to the following file, and if they were identical I would delete (or move to a backup folder) the second file, until they didn't match any longer, and I would move onto the next prefix as the comparator.

The problem with this though I found, is that they aren't always sorted correctly, and I risk deleting the wrong files.

Has anyone had experience with something of this nature? In my head and on VS I can put the pieces all there, but just can't seem to link it together, mainly because I've never ventured into the system.IO class before, but I want to learn!

Any advice is appreciated, and if you want to see my futile attempts I'll gladly share them :P.

Thanks, Nick

You should be able to use Directory.GetFiles to retrieve the filenames. I suspect that your sorting problem is probably due to casing - in C#, string sorts, by default, as case sensitive, but the file system is not.

I'd recommend loading up the list of files, then sorting them yourself, in C#, prior to processing them:

 List<string> files = Directory.GetFiles(myDirectory)
     .Select(file => file.ToLower()) // To lower case
     .OrderBy(file => file) // Sort the files
     .ToList();

 // Process the files here...

Create a dictionary indexed by the three character prefix.

When you reach a file, check the dictionary for a value:

• if none exists, keep the file and add it to the dictionary, where the key is the prefix and the value is the number following the prefix

• if one exists, but has an older "number" value, archive the old one, keep the newer one and update the dictionary to have the new number

• if one exists, but has a newer "number" value, archive the old one, keep the newer one and the dictionary is already up to date at this point.

No sorting necessary.

EDIT: Adding example:

public static void ProcessDirectory(string directoryPath)
    {
        IDictionary<string,string> prefixDictionary = new Dictionary<string, string>();

        if (Directory.Exists(directoryPath))
        {
            foreach(string filePath in Directory.GetFiles(directoryPath))
            {
                string fileName = Path.GetFileName(filePath);
                string fileDirectory = Path.GetDirectoryName(filePath);
                if (fileName.Length>=3)
                {                        
                    string prefix = fileName.Substring(0, 3);
                    string rightPart = fileName.Substring(3, fileName.Length - 3);
                    if (!prefixDictionary.ContainsKey(prefix))
                    {
                        prefixDictionary[prefix] = rightPart;
                    }
                    else
                    {
                        string fileToArchive = null;
                        string storedRightPart = prefixDictionary[prefix];
                        // using string compare, but you could test file date or
                        // or parse the right part as a number if you only cared about
                        // files with numbers on the right.
                        if (String.Compare(storedRightPart,rightPart)<0)
                        {
                            prefixDictionary[prefix] = rightPart;
                            fileToArchive = Path.Combine(fileDirectory,prefix+storedRightPart);
                        }
                        else
                        {
                            fileToArchive = filePath;
                        }

                        if (fileToArchive != null)
                        {
                            // perform the archive here
                        }
                    }
                }
            }
        }
    }

You get get an array of FileInfo objects, which contain a lot of the metadata about the files, which would let you sort them. It also allows you to delete.

DirectoryInfo dir = new DirectoryInfo(@"C:/yourPath");
FileInfo[] files = dir.GetFiles();

From there, you can sort files by CreationTime or Name or whatever. To delete one, just use the Delete method on the FileInfo class.