DataTable dt = new DataTable();
dt.Columns.AddRange(new DataColumn[] { new DataColumn("name", typeof(string)),
                                        new DataColumn("sex", typeof(string)),
                                        new DataColumn("score", typeof(int)) });
dt.Rows.Add(new object[] { "张三","男",1 });
dt.Rows.Add(new object[] { "张三","男",4 });
dt.Rows.Add(new object[] { "李四","男",100 });
dt.Rows.Add(new object[] { "李四","女",90 });
dt.Rows.Add(new object[] { "王五","女",77 });
DataTable dtResult = dt.Clone();
for (int i = 0; i < dt.Rows.Count; )
{
    DataRow dr = dtResult.NewRow();
    string name = dt.Rows[i]["name"].ToString();
    string sex = dt.Rows[i]["sex"].ToString();
    dr["name"] = name;
    dr["sex"] = sex;
    int score = 0;
    //内层也是循环同一个表，当遇到不同的name时跳出内层循环
    for (; i < dt.Rows.Count; )
    {
        if (name == dt.Rows[i]["name"].ToString()&&name == dt.Rows[i]["sex"].ToString())
        {
            score += Convert.ToInt32(dt.Rows[i]["score"]);
            dr["score"] = score;
            i++;
        }
        else
        {
            break;
        }
    }
    dtResult.Rows.Add(dr);
}

DataTable dt = new DataTable();
dt.Columns.AddRange(new DataColumn[] { new DataColumn("name", typeof(string)),
                                         new DataColumn("sex", typeof(string)),
                                         new DataColumn("score", typeof(int)) });
dt.Rows.Add(new object[] { "张三","男",1 });
dt.Rows.Add(new object[] { "张三","男",4 });
dt.Rows.Add(new object[] { "李四","男",100 });
dt.Rows.Add(new object[] { "李四","女",90 });
dt.Rows.Add(new object[] { "王五","女",77 });
DataTable dtResult = dt.Clone();
DataTable dtName = dt.DefaultView.ToTable(true, "name","sex");
for (int i = 0; i < dtName.Rows.Count; i++)
{
    DataRow[] rows = dt.Select("name=‘" + dtName.Rows[i][0] + "‘ and sex=‘" + dtName.Rows[i][1] + "‘");
    //temp用来存储筛选出来的数据
    DataTable temp = dtResult.Clone();
    foreach (DataRow row in rows)
    {
        temp.Rows.Add(row.ItemArray);
    }

    DataRow dr = dtResult.NewRow();
    dr[0] = dtName.Rows[i][0].ToString();
    dr[1] = temp.Compute("sum(score)", "");
    dtResult.Rows.Add(dr);
} 

3、使用linq to DataTable group by实现

var query = from t in dt.AsEnumerable()
            group t by new { t1 = t.Field<string>("name"), t2 = t.Field<string>("sex") } into m
            select new
            {
                name = m.Key.t1,
                sex = m.Key.t2,
                score = m.Sum(n => n.Field<decimal>("score"))
            };
if (query.ToList().Count > 0)
{
    query.ToList().ForEach(q =>
    {
        Console.WriteLine(q.name + "," + q.sex + "," + q.score);
    });
}