Creating multiple files based on DataRow content

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C#

file

DataRow

I have an application that converts .xlsx files into .txt files. On one of my files, there are multiple agencies I need to separate and write the similar ones to their own file. For example, There is an agency 55 and agency 99. There are several entries of each and not necessarily in order. I need a file for each agency with only entries in each file that have the correlating agency number.

Now the kicker is I won't know what the agency number is or how long it will be on any given row. I have figured out how to get the agency number for each row I have, but I need help on how to store those values and use them to write a file that has only those agency numbers in them.

Here is what I have so far to get the agency number I need and my initial code that just wrote to one file.

if (ddlType.SelectedValue == "authorize.net")
        {
            string filename = FileUpload1.FileName.ToString();
            FileUpload1.SaveAs("C:\\inetpub\\temp\\" + filename);

            if (filename != "")
            {
                FileInfo file = new FileInfo("C:\\inetpub\\temp\\" + filename);

                if (file.Exists)
                {
                    DataTable dt = new DataTable();
                    using (TextReader tr = File.OpenText("C:\\inetpub\\temp\\" + filename))
                    {
                            string line;
                            while ((line = tr.ReadLine()) != null)
                            {
                                string[] items = line.Split('\t');
                                if (dt.Columns.Count == 0)
                                {
                                    // Create the data columns for the data table based on the number of items 
                                    // on the first line of the file
                                    for (int i = 0; i < items.Length; i++)
                                    {
                                        dt.Columns.Add(new DataColumn("Column" + i, typeof(string)));
                                    }
                                }
                                dt.Rows.Add(items);
                            }
                            tr.Close();
                    }
                    ////Print out all the values 
                    string file99 = "C:\\inetpub\\temp\\99-Authorize.Net - " + date1 + " @ " + date2 + ".ach";
                    StreamWriter sw2 = new StreamWriter(file99, true);

                    foreach (DataRow dr in dt.Rows)
                    {
                        string agencyNumber;
                        int index = dr[12].ToString().IndexOf("|");
                        if (index > 0)
                        {
                            agencyNumber = dr[12].ToString().Substring(0, index);
                        }
                        if (dr[0].ToString() != "2")
                        {
                            if (dr[9].ToString() != "Total Amount")
                            {
                                sw2.Write("6                            ");
                                sw2.Write(dr[9].ToString().Replace(".", "").Replace(",", "").PadLeft(10, '0'));
                                sw2.Write((dr[12].ToString().Remove(0, index)).PadRight(15, ' '));
                                sw2.Write((dr[13].ToString() + " " + dr[14].ToString()).PadRight(40));
                                sw2.Write(sw2.NewLine);
                            }
                        }
                    }
                    sw2.Write("9");
                    sw2.Write(sw2.NewLine);
                    sw2.Close();
                    Session.Add("DatedFileName2", file99);
                }
                LinkButton1.Visible = true;
                LinkButton2.Visible = true;
            }
        }