groupby时不能隐式转换类型

Question

I get this error when I try to group by CellID :

Cannot implicitly convert type 'System.Collections.Generic.List System.Linq.IGrouping int,p2pControllerLogAnalyser.Models.GSMData' to 'System.Collections.Generic.List p2pControllerLogAnalyser.Models.GSMData'

public List<GSMData> GetCellID()
{
    return Gsmdata.GroupBy(x => x.CellID).ToList();
}

What am I doing wrong and how can I fix it?

Answer 1

If you really need to do this, though I can't imagine why, you'll need to flatten the per-group enumerables into a single list using SelectMany :

public List<GSMData> GetCellID()
{
    return Gsmdata
        .GroupBy(x => x.CellID)
        .SelectMany(gr => gr)
        .ToList();
}

Of course, this looks like you are trying to batch items with the same CellID together, so you could always simply order it:

public List<GSMData> GetCellID()
{
    return Gsmdata
        .OrderBy(x => x.CellID)
        .ToList();
}

---

Further to your comments, distinct CellID values can be returned thus:

 return Gsmdata.Select(x => x.CellID).Distinct(); 

If you wish to return an ID and a count of grouped data, you can bundle that into an anonymous type:

 return Gsmdata .GroupBy(x => x.CellID) .Select(gr => new { CellID = gr.Key, Count = gr.Count() }); 

Though if you are returning this from a method I'd make a discoverable type and not use an anonymous type.

Answer 2

The problem is that GroupBy returns a grouped collection, in this case System.Collections.Generic.List<System.Linq.IGrouping<int, p2pControllerLogAnalyser.Models.GSMData>> . Your method returns a List<GSMData> .

In order to fix this, you need to adjust your method declaration and/or your Linq query so that the types match.

From your comments, I understand that you want to return a list of the distinct cell ids. You can do this by changing both the method declaration and the Linq query (I'm assuming that CellID is of type int based upon the type in the IGrouping):

public List<int> GetCellID()
{
    return Gsmdata.Select(x => x.CellID)
                  .Distinct().ToList();
}

Answer 3

if i understand right you need something like this

var result = (from gdata in Gsmdata
              group gdata by gbata.CellID into g
              select new Result{
                  CellID = g.Key,
                  Meters = g.Sum(i=>i.Meter)
              }
             ).ToList();

where Result is

public class Result{
    public /*type your CellID */ CellID;
    public /*type your Meter */  Meters;
}