How to compare two Dictionaries in C#

If you’ve already checked that the keys are the same, you can just use:

var dict3 = dict2.Where(entry => dict1[entry.Key] != entry.Value)
                 .ToDictionary(entry => entry.Key, entry => entry.Value);

To explain, this will:

• Iterate over the key/value pairs in dict2
• For each entry, look up the value in dict1 and filter out any entries where the two values are the same
• Form a dictionary from the remaining entries (i.e. the ones where the dict1 value is different) by taking the key and value from each pair just as they appear in dict2.

Note that this avoids relying on the equality of KeyValuePair<TKey, TValue> – it might be okay to rely on that, but personally I find this clearer. (It will also work when you’re using a custom equality comparer for the dictionary keys – although you’d need to pass that to ToDictionary, too.)