Efficient DataTable Group Por

Question

Me gustaría realizar una consulta agregada en una DataTable para crear otra DataTable. No puedo alterar el SQL que se usa para crear la DataTable inicial.

original DataTable: (todo es un int)

TeamID | MemberID 
-------|----------- 
1  | 1 
1  | 2 
1  | 3 
2  | 4 
2  | 5 

resultado deseado:

TeamID | MemberIDCount 
-------|-------------- 
1  | 3 
2  | 2 

Si se tratara de SQL tan sólo pudiera hacer

Select TeamID, Count(*) From Table Group By TeamID 

pero en mi solicitud, la única forma en que sé cómo manejar esto sería algo como esto:

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); 
    } 
} 

¿Hay una manera mejor?

Answer 1

Es posible utilizar 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); 

Answer 2

public DataTable GroupBy(string i_sGroupByColumn, string i_sAggregateColumn, DataTable i_dSourceTable) 
{ 

    DataView dv = new DataView(i_dSourceTable); 

    //getting distinct values for group column 
    DataTable dtGroup = dv.ToTable(true, new string[] { i_sGroupByColumn }); 

    //adding column for the row count 
    dtGroup.Columns.Add("Count", typeof(int)); 

    //looping thru distinct values for the group, counting 
    foreach (DataRow dr in dtGroup.Rows) { 
     dr["Count"] = i_dSourceTable.Compute("Count(" + i_sAggregateColumn + ")", i_sGroupByColumn + " = '" + dr[i_sGroupByColumn] + "'"); 
    } 

    //returning grouped/counted result 
    return dtGroup; 
} 

Ejemplo:

DataTable desiredResult = GroupBy("TeamID", "MemberID", dt); 

Answer 3

Agrupar por en LINQ

var listInfo = (from infoMember in context.Members 
       where infoMember.TeamID == TeamID 
       group infoMember by new 
       { infoMember.TeamID, infoMember.MemberIDCount } into newInfoMemeber 
       select new ClassName 
       { 
        TeamID = newInfo.Key.TeamID, 
        MemberIDCount = newInfo.Key.MemberIDCOunt, 
        Count = newInfo.Count(), 
        TotalCount = (from infoMemeber2 in context.Members 
           where infoMemeber2.TeamID== TeamID 
           select infoResult2).Count() 
       }).AsEnumerable();