Combining elements in the same list

Question

suppose I have a list that comes from a database like this:

List<Item> list =
{
    new Item
    {
        TypeID = 2,
        Count = 5
    },
    new Item
    {
        TypeID = 2,
        Count = 7
    },
    new Item
    {
        TypeID = 5,
        Count = 2
    }
};

I would like to sum up all elements with the same TypeID so that I have a final result list with two elements only:

List<Item> list =
{
    new Item
    {
        TypeID = 2,
        Count = 12
    },
    new Item
    {
        TypeID = 5,
        Count = 2
    }
};

How can I achive this using LINQ?
Cheers
Simon

Nothing so far. Well it would be easy using foreach but I want to have in with LINQ. — Simon Linder
– Simon Linder, Commented Sep 28, 2012 at 9:47

L.B · Accepted Answer · 2012-09-28 09:41:15Z

7

list.GroupBy(x=>x.TypeID)
    .Select(x=>new Item(){TypeID=x.Key,Count=x.Sum(y=>y.Count) })
    .ToList();

answered Sep 28, 2012 at 9:41

L.B

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Comments

cuongle · Accepted Answer · 2012-09-28 09:46:58Z

5

You can use GroupBy to group by TypeID first and then do Sum on each group:

var result = list.GroupBy(x => x.TypeID)
                 .Select(g => new Item() { 
                                  TypeId = g.Key, 
                                  Count = g.Sum(x => x.Count)
                         })
                 .ToList();

edited Sep 28, 2012 at 9:46

answered Sep 28, 2012 at 9:41

cuongle

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1 Comment

Simon Linder Over a year ago

Both answers are correct. But Cuong Le war faster... Thx a lot, exactly what I wanted to have.

Sender · Accepted Answer · 2012-09-28 09:42:42Z

0

Linq extension method Union.

var mergedList = list1.Union(list2).ToList();

answered Sep 28, 2012 at 9:42

Sender

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