高效的数据表组通过 [英] Efficient DataTable Group By
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问题描述
我想在一个DataTable创建其他DataTable执行聚合查询。我不能改变SQL被用来创建初始数据表。
I would like to perform an aggregate query on a DataTable to create another DataTable. I cannot alter the SQL being used to create the initial DataTable.
原始数据表:(一切都是一个int)
Original DataTable: (everything is an int)
TeamID | MemberID
-------|-----------
1 | 1
1 | 2
1 | 3
2 | 4
2 | 5
期望的结果:
TeamID | MemberIDCount
-------|--------------
1 | 3
2 | 2
如果它是SQL我只是做
If it were SQL I could just do
Select TeamID, Count(*) From Table Group By TeamID
但在我的应用程序,只有这样,我知道如何处理这将是这样的:
but in my application, the only way I know how to handle this would be something like this:
Dictionary<int,int> d = new Dictionary<int,int>();
foreach (DataRow dr in dt.Rows)
{
if (d.ContainsKey(dr.ID))
{
d[dr.ID] = d[dr.ID] + 1;
}
else
{
d.Add(dr.ID, 1);
}
}
有没有更好的办法?
Is there a better way?
推荐答案
您可以使用Linq。
var result = from row in dt.AsEnumerable()
group row by row.Field<int>("TeamID") into grp
select new
{
TeamID = grp.Key,
MemberCount = grp.Count()
};
foreach (var t in result)
Console.WriteLine(t.TeamID + " " + t.MemberCount);
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