Convert var to List<T> in c#

问题

I am unable to convert back var to List<CustomObject>.

private void PopulateChart(List<CustomObject> rawData)
 {
   var groupedByCategory1 = rawData.GroupBy(co => co.Category1)
   //List<CustomObject> data = groupedByCategory1.GroupBy(co => co.Category1).ToList();    
 }

Note: From rawData I have to get Groupby data. using that result again I have to group the data.

回答1:

Linq GroupBy returns System.Linq.IQueryable<IGrouping<TKey,TSource>>. So, you should select some data from groups:

List<CustomObject> data = groupedByCategory1
     .GroupBy(co => co.Category1)
     .Select(grp => new CustomObject 
          {
              Category1 = grp.Key
          }
     .ToList(); 

回答2:

 var data = groupedByCategory1
         .GroupBy(co => co.Category1)
         .Select(grp => new 
              {
                  Category1 = grp.Key// This is the key that you used to group
                  groupList=grp.ToList();//This will be the list of CustomObject
              }
         .ToList(); 

Actually, GroupBy groups your list into another list where Category1 is same.

You can access it as shown below

foreach (var group in data)
{// This group is List<CustomObject>. If you don't want to access it like this, whats the meaning of group by?
  var groupKey=group.Category1;
  foreach(CustomObject myObj in group.groupList)
   {

   }
}

回答3:

Have you tried

var groupedByCategory1 = rawData
   .GroupBy(co => co.Category1)    
   .SelectMany(c => c)
   .ToList();

来源：https://stackoverflow.com/questions/22627426/convert-var-to-listt-in-c-sharp