How do I convert a Dictionary to a Lookup? [duplicate]

问题

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LINQ Convert Dictionary to Lookup (2 answers)

Closed 5 years ago.

I have a Dictionary that has a signature: Dictionary<int, List<string>>. I'd like to convert it to a Lookup with a signature: Lookup<int, string>.

I tried:

Lookup<int, string> loginGroups = mapADToRole.ToLookup(ad => ad.Value, ad => ad.Key);

But that is not working so well.

回答1:

You could use:

var lookup = dictionary.SelectMany(p => p.Value
                                         .Select(x => new { p.Key, Value = x}))
                       .ToLookup(pair => pair.Key, pair => pair.Value);

(You could use KeyValuePair instead of an anonymous type - I mostly didn't for formatting reasons.)

It's pretty ugly, but it would work. Can you replace whatever code created the dictionary to start with though? That would probably be cleaner.

来源：https://stackoverflow.com/questions/10420228/how-do-i-convert-a-dictionary-to-a-lookup