Merging dictionaries in C#

Question

What\'s the best way to merge 2 or more dictionaries (Dictionary) in C#? (3.0 features like LINQ are fine).

I\'m thinking of a method signa

Answer 1

Option 1 : This depends on what you want to happen if you are sure that you don't have duplicate key in both dictionaries. than you could do:

var result = dictionary1.Union(dictionary2).ToDictionary(k => k.Key, v => v.Value)

Note : This will throw error if you get any duplicate keys in dictionaries.

Option 2 : If you can have duplicate key then you'll have to handle duplicate key with the using of where clause.

var result = dictionary1.Union(dictionary2.Where(k => !dictionary1.ContainsKey(k.Key))).ToDictionary(k => k.Key, v => v.Value)

Note : It will not get duplicate key. if there will be any duplicate key than it will get dictionary1's key.

Option 3 : If you want to use ToLookup. then you will get a lookup which can have multiple values per key. You could convert that lookup to a dictionary:

var result = dictionaries.SelectMany(dict => dict)
                         .ToLookup(pair => pair.Key, pair => pair.Value)
                         .ToDictionary(group => group.Key, group => group.First());