GROUP by 方法 Ｃ#

1、用两层循环计算，前提条件是数据已经按分组的列排好序的。

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);

}

dtResult中的数据即是最终结果。

2、 借助DataTable的Compute方法，DataTable中数据不用事先排好序。

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);     }); }

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收集整理，非原创