Fastest way to Compare two Dictionaries using foreach and .contains to find unique and non-unique data

Question

I currently have 2 dictionaries with ard 30,000keys.

I am currently using two foreach loops to find the unique keys in dict1. And I write the unique keys in dict2 to another dictionary(3).

If the keys match i perform a check to see if the value are the same. And print if they are not the same.

Is it better to use foreach, it seems to be affecting the performance. Is there any other faster solution or built in functions? Ir shd I try the dict.contains method.

---

Dict1                    Dict2

Keys    Values           Keys     Values        
S0111   00000            S0000    00010
S0000   00010            S0020    00015
S0020   00015            S0040    00150
S0040   00200            S0050    00250

---

        foreach (KeyValuePair<string, string> sourceRow in sourceData)
        {
            foreach (KeyValuePair<string, string> dumpRow in dumpData)
            {
                // A in C, skip
                if (sourceRow.Key == dumpRow.Key)
                {
                    Is_Unique_Address = false;

                    if (sourceRow.Value != dumpRow.Value)
                    {
                        Data_Mismatch_Criteria(sourceRow.Key, sourceRow.Value, dumpRow.Key, dumpRow.Value);
                    }

                }
            }
        }

Answer 1

This code enables you to select keys from dict2, which are not contained in dict1.

var dict1 = new Dictionary<string, string>();
var dict2 = new Dictionary<string, string>();

// Add data to both dictionaries

var uniqueKeys = dict2.Keys.Except(dict1.Keys);

Is that what you need?

EDIT: Please note, that the code above selects all keys from dict2 not contained in dict1. If you need to check that both dictionaries have different sets of keys (and I assume that it may be the case), then you can use:

var areTheSame = dict2.Keys.Any(x => !dict1.ContainsKey(x))
|| dict1.Keys.Any(x => !dict2.ContainsKey(x));

EDIT 2: After OP edit, I now know what you need:

var differentValues = dict2.Where(pair => dict1.ContainsKey(pair.Key))
     .Select(pair => new
     {
         ValueA = pair.Value,
         ValueB = dict1[pair.Key],
         Key = pair.Key
     })
     .Where(x => x.ValueA != x.ValueB)
     .ToList();

foreach (var differentValue in differentValues)
{
    Console.WriteLine(differentValue);
}