public static void ReadFile(Stream mailStream, Stream infoStream, XlsxWriter xlsx) { if (allMailSheetNames.Any(sheetName => xlsx.HasWorksheet(sheetName))) { return; } var mailInfos = Record.GetRecords(infoStream, "ssss", new string[] { "Mail ID", "Order in Idol Folder", "Idol ID", "" }) .ToDictionary(record => (short)record[0]); var mails = Record.GetRecords(mailStream, mailFormat, mailHeadings); foreach (var record in mails) { short mailID = (short)record[0]; short idolID = (short)mailInfos[mailID][2]; xlsx.AppendRow(mailSheetNameArray[idolID], record); } }