高效的数据表分组依据 [英] Efficient DataTable Group By
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问题描述
我想对 DataTable 执行聚合查询以创建另一个 DataTable.我无法更改用于创建初始 DataTable 的 SQL.
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:(一切都是整数)
Original DataTable: (everything is an int)
TeamID | MemberID
-------|-----------
1 | 1
1 | 2
1 | 3
2 | 4
2 | 5
想要的结果:
TeamID | MemberIDCount
-------|--------------
1 | 3
2 | 2
如果是 SQL 我就可以了
If it were SQL I could just do
Select TeamID, Count(*) From Table Group By TeamID
但在我的应用程序中,我知道如何处理这个问题的唯一方法是这样的:
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);
}
}
有更好的方法吗?
推荐答案
您可以使用 Linq.
You may use 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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