How to make sublist of existing list having common items?

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C#4.0

I have list(A) of 2,30,000 items where 1st item in list is (3,1110000000) here in this example 3 is sum of number 1110000000. and I sorted this list in descending order according to sum and now my 1st item is (57,9657551955). now there are many numbers whose sum is 57 and so on then dump all numbers whose sum is 57 into a file named "57.CSV" and so on. now after sorting the list in descending order I found 57 sum from 0th index to 121th index , 56 sum from 122th index to 178th index. Now i want to create lists from list(A) for all sums 57 , 56 and so on. How to do this?

Please suggest.

What I have tried:

using (StreamReader sr = new StreamReader(fs))
                    {
                        string barcode_data = sr.ReadToEnd().Replace("\r\n", ",");
                        string[] Allbarcodes = barcode_data.Split(',');
                        int counter = 0;

                        for (int i = 0; i < Allbarcodes.Length - 1; i++)
                        {
                            if (!string.IsNullOrEmpty(Allbarcodes[i]))
                            {
                                long sumOfnum = Summation(Convert.ToInt64(Allbarcodes[i]));
                                barcodeList.Add(sumOfnum + "," + Allbarcodes[i]);
                            }
                        }
                        Array.Clear(Allbarcodes, 0, Allbarcodes.Length);
                        label1.Text = counter++.ToString();

                        result = barcodeList.Select(m => new { value = int.Parse(m.Substring(0, m.IndexOf(','))), item = m }).
                                     OrderByDescending(m => m.value).Select(m => m.item).ToList();
////list result contains all items and have to make sublists of it//// 
                        sr.Close();
                        sr.Dispose();
                    }