CODEWITHSUNDEEP
linqdictionary
Atari2600
Atari2600

Reputation: 2813

LINQ Group By into a Dictionary Object

I am trying to use LINQ to create a Dictionary<string, List<CustomObject>> from a List<CustomObject>. I can get this to work using "var", but I don't want to use anonymous types. Here is what I have 

var x = (from CustomObject o in ListOfCustomObjects
      group o by o.PropertyName into t
      select t.ToList());

I have also tried using Cast<>() from the LINQ library once I have x, but I get compile problems to the effect of it being an invalid cast.

Upvotes: 258

Views: 205628

Answers (5)

Don Feto
Don Feto

Reputation: 1524

This might help you if you to Get a Count of words. if you want a key and a list of items just modify the code to have the value be group.ToList()

    var s1 = "the best italian resturant enjoy the best pasta";    
    var D1Count = s1.ToLower().Split(' ').GroupBy(e => e).Select(group => new { key = group.Key, value = group.Count() }).ToDictionary(e => e.key, z => z.value);


//show the results
                    Console.WriteLine(D1Count["the"]);
                    foreach (var item in D1Count)
                    {
                        Console.WriteLine(item.Key +" "+ item.Value);
                    }

Upvotes: -1

Leo Barbas
Leo Barbas

Reputation: 139

The following worked for me.

var temp = ctx.Set<DbTable>()
  .GroupBy(g => new { g.id })
  .ToDictionary(d => d.Key.id);

Upvotes: -3

Michael Blackburn
Michael Blackburn

Reputation: 3229

For @atari2600, this is what the answer would look like using ToLookup in lambda syntax:

var x = listOfCustomObjects
    .GroupBy(o => o.PropertyName)
    .ToLookup(customObject => customObject);

Basically, it takes the IGrouping and materializes it for you into a dictionary of lists, with the values of PropertyName as the key.

Upvotes: 3

RuudvK
RuudvK

Reputation: 635

I cannot comment on @Michael Blackburn, but I guess you got the downvote because the GroupBy is not necessary in this case.

Use it like:

var lookupOfCustomObjects = listOfCustomObjects.ToLookup(o=>o.PropertyName);
var listWithAllCustomObjectsWithPropertyName = lookupOfCustomObjects[propertyName]

Additionally, I've seen this perform way better than when using GroupBy().ToDictionary().

Upvotes: 39

Yuriy Faktorovich
Yuriy Faktorovich

Reputation: 68737

Dictionary<string, List<CustomObject>> myDictionary = ListOfCustomObjects
    .GroupBy(o => o.PropertyName)
    .ToDictionary(g => g.Key, g => g.ToList());

Upvotes: 567

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