LINQ Getting Unique items from a List within a List

Question

I have a List of type MyObject with a definition below:

class MyObject {
     public string ListName { get; set; }
     public IEnumerable<OtherObject> ObjectList { get; set;}
}

Given a List of type MyObject, using LINQ what expression should I use to get all distinct OtherObject?

What I was planning to do was loop each MyObject and get the distinct OtherObject from the ObjectList property, but then I need to get the distinct across the list.

Please note that if: MyObject[0].Objectlist[0] == 'ItemA' and MyObject[1].Objectlist[0] == 'ItemA' it will still return a single instance of ItemA. This code is just a representation only. This is not how I access my objects, by the way.

http://stackoverflow.com/questions/1300088/distinct-with-lambda might this be something worth looking at. — Thomas Lindvall, Jul 12 '12 at 08:25

Rich O'Kelly · Accepted Answer · 2012-07-12T08:29:41.617

10

You can achieve this simply using Set logic. C# has a nice implementation in the form of HashSet:

var set = new HashSet<OtherObject>(myObjects.SelectMany(mo => mo.ObjectList));

Or if you prefer deferred execution, you can use the LINQ Distinct method:

var distinct = myObjects.SelectMany(mo => mo.ObjectList).Distinct();

edited Jul 12 '12 at 08:29

answered Jul 12 '12 at 08:24

Rich O'Kelly

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Thank you! I have an object that is a property of a bigger object, that is in a list, that is in a list. Was able to get a unique list by doing `data.SelectMany(d => d.Refs).Select(r => r.MyObject).Distinct()` which is way simpler than using a `.ForEach()`. – jwatts1980 Feb 12 '14 at 18:15

score 3 · Answer 2 · edited May 23 '17 at 11:54

3

How about:

var l = new List<MyObject>(...);
var unique = l.SelectMany(j => j.ObjectList).Distinct();

You can use the technique from Distinct() with lambda? to alter how you decide if an object is distinct from another.

edited May 23 '17 at 11:54

Community

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answered Jul 12 '12 at 08:26

mdm

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LINQ Getting Unique items from a List within a List

2 Answers2

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