CODEWITHSUNDEEP
c#linqgroup-by
newbie_86
newbie_86

Reputation: 4610

Group by and select in LINQ

I want to be able to group a list of items by a particular field (id) and then extract a dictionary of id,code pairs. I then need to access the id and code pairs to do some logic. how can i do this using linq?

e.g. 

Id Code Send
1  500  1 
1  501  0
2  600  1
2  601  0
2  602  0
3  700  0
3  701  1
3  702  0
3  703  1

Expected Result -

1 500,501
2 600,601,602
3 700, 701, 702, 703

This is what i have so far - struggling to work out how to get just the codes into a dictionary:

from i in items 
group i by i.Id into g
select new Dictionary<Guid, List<long>>
   {
     g.Key, g.ToList()
   }

Upvotes: 1

Views: 104

Answers (3)

Enigmativity
Enigmativity

Reputation: 117019

It seems to me that LINQ has an operator that does this already.

ILookup<Guid, long> res = items.ToLookup(i => i.Id, i => i.Code);

Upvotes: 0

Sam Leach
Sam Leach

Reputation: 12956

the last part 

g.ToList()

needs to be

g.Select(c => c.Code).ToList()

Upvotes: 1

Sergey Kalinichenko
Sergey Kalinichenko

Reputation: 726479

You can do it like this:

var res = items
    .GroupBy(i => i.Id)
    .ToDictionary(
        g => g.Key
    ,   g => g.Select(v => v.Code).ToList()
    );

Your solution was close - you needed to add a selection of Code to complete it.

Upvotes: 1

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