Combining multiple dictionaries into one

Question

Let's assume I have two variables which both are of type Dictionary<int, int>.

Dictionary<int, int> d1 = new Dictionary<int, int> { ... };
Dictionary<int, int> d2 = new Dictionary<int, int> { ... };

Both dictionaries could potentionally contain the same keys.

I want them to combine into a single Dictionary<int, int> combinedDictionary.

What would be an elegant way to do this?

I've tried the following:

var combinedDictionary = d1.Concat(d2.Where(x => !d1.Keys.Contains(x.Key)));

But unfortunately, when trying to return this combined variable I get the following error:

Cannot convert expression type 'System.Collections.Generic.IEnumerable>' to return type 'System.Collections.Generic.Dictionary'.

Is it possible to safely cast it like this?

return (Dictionary<int, int>) combinedDictionary;

thanks in advance!

https://stackoverflow.com/questions/294138/merging-dictionaries-in-c-sharp — Chetan Ranpariya, Jun 05 '18 at 11:48
Sure, there is lots of code out there to merge dictionaries. Those examples do not explain why this approach isn't working. — Amy B, Jun 05 '18 at 11:55

Amy B · Accepted Answer · 2018-06-05T11:50:57.193

1

Concat returns an IEnumerable<KeyValuePair<TKey, TValue>>. You want to call ToDictionary to convert that into a Dictionary.

IEnumerable<KeyValuePair<int, int>> combined = d1.Concat(d2.Where(x => !d1.Keys.Contains(x.Key)));
Dictionary<int, int> result = combined.ToDictionary(x => x.Key, x => x.Value);

edited Jun 05 '18 at 11:50

answered Jun 05 '18 at 11:47

Amy B

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@SeM The compiler didn't lie. You can try it too. – Amy B Jun 05 '18 at 11:51
Oopps, I didn't see this part in question `return (Dictionary) combinedDictionary;`, sorry, move on. – SᴇM Jun 05 '18 at 11:55

Combining multiple dictionaries into one

1 Answers1