Select distinct from property which is List

Question

I have a generic list of assets (List<Asset>) and one of the assets properties is called Tags which is a list of strings

How would I do a Linq query to get a distinct list of tags. I tried

assetList.Select(a => a.Tags).Distinct()

but this returns me an IEnumerable<List<string>> instead of an IEnumerable<string>

score 1 · Accepted Answer · answered Feb 14 '14 at 10:30

1

You was close. You need to use Enumerable.SelectMany to select all tags and flatten them into one sequence:

assetList.SelectMany(a => a.Tags).Distinct()

answered Feb 14 '14 at 10:30

Sergey Berezovskiy

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score 0 · Answer 2 · edited May 23 '17 at 12:09

0

assetList.SelecMany(a => a.Tags).Distinct() . correct it

more information about differences Difference Between Select and SelectMany

edited May 23 '17 at 12:09

Community

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answered Feb 14 '14 at 10:31

Eugene P.

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score 0 · Answer 3 · answered Feb 14 '14 at 10:31

Select only takes objects as they are and Tags is a list, so it takes lists. If you need items from these lists, you have to flatten them into one list and then proceed with other operations.

assetList.SelectMany(a => a.Tags).Distinct();

A nice example from MSDN on SelectMany

PetOwner[] petOwners = 
                { new PetOwner { Name="Higa, Sidney", 
                      Pets = new List<string>{ "Scruffy", "Sam" } },
                  new PetOwner { Name="Ashkenazi, Ronen", 
                      Pets = new List<string>{ "Walker", "Sugar" } },
                  new PetOwner { Name="Price, Vernette", 
                      Pets = new List<string>{ "Scratches", "Diesel" } } };

IEnumerable<string> query1 = petOwners.SelectMany(petOwner => petOwner.Pets);

produces the following list

Scruffy, Sam, Walker, Sugar, Scratches, Diesel

Select distinct from property which is List

3 Answers3