本文介绍了高效的 DataTable 分组依据的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
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.
Original DataTable: (everything is an int)
TeamID | MemberID
-------|-----------
1 | 1
1 | 2
1 | 3
2 | 4
2 | 5
Desired result:
TeamID | MemberIDCount
-------|--------------
1 | 3
2 | 2
If it were SQL I could just do
Select TeamID, Count(*) From Table Group By TeamID
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);
}
}
Is there a better way?
解决方案
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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