Create a Dictionary by ignoring repeating keys

0
votes

Let's say I have this Dictionary:

var Dict = Dictionary<Obj, Value>

And I want to create a new one that is:

var Dict2 = Dictionary<Obj.ParentId, Value>

However, there might be objects that have the same ParentId, so that would be a problem when creating a new Dictionary. Any two entries with the same ParentId will have the same Value, so I only care to keep one of the entries. Is there a way to easily do this either through LINQ?

2
c#.netlinq
Which of the entries do you want to keep? The first? By some criteria? – D M
Any would be fine, since they would be identical – Ankad
What are the types of ParentId and Value? You can use Distinct or you might need DistinctBy. – NetMage
ConcurrentDictionary automatically removes duplicate entries – GH DevOps

2 Answers

2
votes

The easiest way to do this is probably imperatively using a loop. In this approach, the last one wins - but, as you say, this shouldn't matter in your case:

var dict2 = new Dictionary<Obj.ParentId, Value>();

foreach (var (key, value) in dict1)
{
    dict2[key.ParentId] = value;
}

You could also do this using LINQ, but it's probably less performant given it has to do the 'distinct' part first:

var dict2 = dict1
    .DistinctBy(x => x.Key.ParentId)
    .ToDictionary(x => x.Key.ParentId, x => x.Value);
1
votes

You can use Linq: query Dict and materialize result as Dict2

var Dict2 = Dict
  .GroupBy(pair => pair.Key.ParentId, pair => pair.Value)
   // Or group.Last().Value or some other logic
  .ToDictionary(group => group.Key, group => group.First().Value);

Or you can try looping:

var Dict2 = Dictionary<Obj.ParentId, Value>();

foreach (var pair in Dict)
  Dict2.TryAdd(pair.Key.ParentId, pair.Value);