linq query to return distinct field values from a list of objects

Question

class obj {     int typeId; //10 types  0-9      string uniqueString; //this is unique } 

Assume there is a list with 100 elements of objs, but only 10 unique typeIDs.

Is it possible to write a LINQ query that returns the 10 unique ints from the list of objs?

Answer 1

objList.Select(o=>o.typeId).Distinct() 

Answer 2

Assuming you want the full object, but only want to deal with distinctness by typeID, there's nothing built into LINQ to make this easy. (If you just want the typeID values, it's easy - project to that with Select and then use the normal Distinct call.)

In MoreLINQ we have the DistinctBy operator which you could use:

var distinct = list.DistinctBy(x => x.typeID); 

This only works for LINQ to Objects though.

You can use a grouping or a lookup, it's just somewhat annoying and inefficient:

var distinct = list.GroupBy(x => x.typeID, (key, group) => group.First());