CODEWITHSUNDEEP
c#listlinqvisual-studio-2008group-by
Willy
Willy

Reputation: 10638

LINQ: Converting grouped list into new list

Initially I have a list of items:

List<Item> mySourceList;

which Item is:

Item Class:

public class Item
{
   public DateTime Date
   {
     get;
     set;
   }
   public string ProviderID
   {
     get;
     set;
   }    
   public List<AnotherClass> listOfitems
   {
     get;       
     set;
   }
   public byte[] Img
   {
     get;
     set;
   }
   // Other properties

   public long GroupID
   {
     get;
     set;
   }
}

I need to group mySourceList by ProviderID and Date so I do below:

var grp = mySourceList .GroupBy(e => new { e.ProviderID, e.Date });

Then I perform some opertions in this grouped list:

int groupId = 1;
foreach (var group in grp)
{
    int id = group.Count() > 1 ? groupId++ : 0;

    // Loop through each item within group
    foreach (var item in group)
        item.GroupID = id;
}

And Finally, I am trying to convert mySourceList list into a new one, this new one must be List again, so I am trying below but it is not working:

List<Item> myDestList = grp.ToList<Item>();

How can I convert to List ?

I am using Visual Studio 2008 and NET Framework 3.5 SP1

Upvotes: 1

Views: 873

Answers (2)

Willy
Willy

Reputation: 10638

I have done below by taking advantage of the operation to update grouped list in the loops:

List<Item> groupedList = new List<Item>();

int groupId = 1;
foreach (var group in grp)
{
    int id = group.Count() > 1 ? groupId++ : 0;

    // Loop through each item within group
    foreach (var item in group)
    {
        item.GroupID = id;
        groupedList.add(Item);
    }
}

myDestList = groupedList;

Fabio solution also works.

Upvotes: 0

Fabio
Fabio

Reputation: 32445

Use SelectMany extension method.
grp is of type IEnumerable<IGrouping<'a, Item>> - so it some kind of list of list.
And you need return flattened list of all items.

List<Item> myDestList = grp.SelectMany(g => g).ToList();

Another approach is using your original list, because your code updating already existed items.

Upvotes: 4

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