s = @"a00001,2
a00001,-1
b00001,1
b00001,1
";
var query = from x in s.Split(new char[] { '\r', '\n' })
                       .Select(x => new { id = x.split(',')[0], value = Convert.ToInt32(x.split(',')[1]) })
           group x by x.id into g
           select new { id = g.Key, value = g.Select(x => x.value).Sum() };
foreach (var item in query)
{
    Console.WriteLine(item.id + "," + item.value);
}

------解决方案--------------------
C# code

        public static List<String[]> ReadTxt(string filePathName)
        {
            List<String[]> ls = new List<String[]>();
            StreamReader fileReader=new   StreamReader(filePathName); 
            string strLine="";
            while (strLine != null)
            {
                strLine = fileReader.ReadLine();
                if (strLine != null && strLine.Length>0)
                {
                    ls.Add(strLine.Split(','));
                    //Debug.WriteLine(strLine);
                }
            }
            fileReader.Close();
            return ls;
        }

------解决方案--------------------
string s = @"a00001,2
                       a00001,-1
                       b00001,1
                       b00001,1";
           var query = from x in s.Split(new string[] { "\r\n" }, StringSplitOptions.None)
                       .Select(x => new { id = x.Split(',')[0].Trim(), value = Convert.ToInt32(x.Split(',')[1]) })
                       group x by x.id into g
                       select new { id = g.Key, value = g.Select(x => x.value).Sum() };  
           foreach (var item in query)  
           {  
               Console.WriteLine(item.id + "," + item.value);  
           }

------解决方案--------------------
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引用:

s = @"a00001,2
a00001,-1
b00001,1
b00001,1
";
var query = from x in s.Split(new char[] { '\r', '\n' })
.Select(x => new { id = x.split(',')[0], value = Convert.ToI……