Merge 2 lists based on one property and concatenate other properties

Question

IList<MyObject> ob1 = {new MyObject {Id = "1", Items = {BananaObject1, BananaObject2}}}  
IList<MyObject> ob2 = { new MyObject {Id = "1", Items = {BananaObject2, BananaObject3}},  
new MyObject {Id = "2", Items = {BananaObject3, BananaObject3}}}

I want to merge the 2 lists such that the resulting list would be

IList<MyObject> ob2 = { new MyObject {Id = "1", Items = {BananaObject1, BananaObject2, BananaObject3}},
new MyObject {Id = "2", Items = {BananaObject3, BananaObject3}}}

So since the id of the first item of the 2 lists were the same, they became one, and one of their property is concatenated.
I can do a for loop to achieve this, but I am looking for a neat best performance linq expression for this.

thank you

If the `Items` in one `MyObject` already contain a duplicate (like in the case of `ob2[1].Items` containing a duplicate of `BananaObject3`), do you want to keep the duplication? — Yacoub Massad, Oct 08 '15 at 18:35
Possible duplicate of [LINQ - Full Outer Join](http://stackoverflow.com/questions/5489987/linq-full-outer-join) — Robert McKee, Oct 08 '15 at 18:47

Jakub Lortz · Accepted Answer · 2015-10-08T18:27:37.113

6

Concat the lists together, GroupBy Id property, SelectMany to get the merged list of items:

ob1.Concat(ob2)
   .GroupBy(o => o.Id)
   .Select(g => new MyObject() 
   { 
      Id = g.Key, 
      Items = g.SelectMany(o => o.Items ).Distinct().ToList()
   });

edited Oct 08 '15 at 18:27

answered Oct 08 '15 at 18:22

Jakub Lortz

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I think you should use `Concat` here, not `Union`. There's not going to be any deduplication unless the same `MyObject` is added twice. – Asad Saeeduddin Oct 08 '15 at 18:25
As per the question `g.SelectMany(o => o.Items ).Distinct().ToList()` – Arghya C Oct 08 '15 at 18:25
I agree with both of the above comments. – Jason Boyd Oct 08 '15 at 18:26
Right, both comments included in the answer. Thanks! – Jakub Lortz Oct 08 '15 at 18:28

Robert McKee · Answer 2 · 2015-10-08T18:40:38.133

0

Use MoreLINQ:

obj1.FullGroupJoin(obj2, 
  a=>a.Id,
  b=>b.Id,
  (id,a,b)=>new {id=id,Items=a.Items.Union(b.Items)},
  new {id=-1, Items=new List<string>()}, //Default for left side
  new {id=-2, Items=new List<string>()});//Default for right side

edited Oct 08 '15 at 18:40

answered Oct 08 '15 at 18:28

Robert McKee

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Sorry, I guess FullGroupJoin hasn't made it into the main branch yet, but here's the code: https://github.com/fsateler/MoreLINQ/blob/full-outer/MoreLinq/FullGroupJoin.cs – Robert McKee Oct 08 '15 at 18:41
Another answer is available here as well: http://stackoverflow.com/questions/5489987/linq-full-outer-join – Robert McKee Oct 08 '15 at 18:46

Merge 2 lists based on one property and concatenate other properties

2 Answers2