Question

I’m creating a tool that is supposed to concatenate docs that contain the same name.

example: C_BA_20000_1.pdf and C_BA_20000_2.pdf
These files should be grouped in one list.
That tool runs on a directory lets say

//directory of pdf files
  DirectoryInfo dirInfo = new DirectoryInfo(@"C:\Users\derp\Desktop");

  FileInfo[] fileInfos = dirInfo.GetFiles("*.pdf");
  

foreach (FileInfo info in fileInfos)

I want to create an ArrayList that contains filenames of the same name

ArrayList list = new ArrayList();
 list.Add(info.FullName);

and then have a list that contains all the ArrayLists of similar docs.

 List<ArrayList> bigList = new List<ArrayList>();

So my question, how can I group files that contains same name and put them in the same list.

EDIT:
Files have the same pattern in their names AB_CDEFG_i
where i is a number and can be from 1-n. Files with the same name should have only different number at the end.

AB_CDEFG_1

AB_CDEFG_2

HI_JKLM_1

Output should be:

List 1: AB_CDEFG_1 and AB_CDEFG_2

List 2: HI_JKLM_1

Answer 1

Create method which extracts ‘same’ part of file name. E.g.

public string GetRawName(string fileName)
{
    int index = fileName.LastIndexOf("_");
    return fileName.Substring(0, index);
}

And use this method for grouping:

var bigList = Directory.EnumerateFiles(@"C:\Users\derp\Desktop", "*.pdf")
                       .GroupBy(file => GetRawName(file))
                       .Select(g => g.ToList())
                       .ToList();

This will return List<List<string>> (without ArrayList).

UPDATE Here is regular expression, which will work with all kind of files, whether they have number at the end, or not

public string GetRawName(string file)
{
    string name = Path.GetFileNameWithoutExtension(file);
    return Regex.Replace(name, @"(_\d+)?$", "")
}

Grouping:

var bigList = Directory.EnumerateFiles(@"C:\Users\derp\Desktop", "*.pdf")
                       .GroupBy(GetRawName)
                       .Select(g => g.ToList())
                       .ToList();