LINQ Convert Dictionary to Lookup

Question

I have a variable of type Dictionary>
I want to convert it to a Lookup.

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Answer 1

Not an answer for the question, but I think this is related information and should be posted here.

There is some edge cases you should take into account. All of them about items of dictionary, which have key, but don't have value.

This is expected behavior. Dictionary and Lookup designed for different purposes.

var dic = new Dictionary> { [true] = null };
var lookup = dic.ToLookup();

Assert.AreEqual(1, dic.Count);
Assert.AreEqual(0, lookup.Count);

Assert.IsTrue(dic.ContainsKey(true));
Assert.IsFalse(lookup.Contains(true));

Assert.IsFalse(dic.ContainsKey(false));
Assert.IsFalse(lookup.Contains(false));

dic[false] -> Exception
lookup[false] -> bool?[0]