using System;

using System.Linq;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        Dictionary<string, object> d1 = new Dictionary<string, object> {

            { "d1", "d1" },

            { "d2", "x" } // This is the only difference

        };

        Dictionary<string, object> d2 = new Dictionary<string, object> {

            { "d1", "d1" },

            { "d2", "d2" }

        };

        GetDifferent(d1, d2).ForEach(d => {

            Console.WriteLine(d);

        });

    }

    private static List<string> GetDifferent(Dictionary<string, object> currentValues, Dictionary<string, object> previousValues)

    {

        var changed = currentValues

                      .Where(k => previousValues.Any(p => p.Key == k.Key && !AreValueEquals(k.Value, p.Value)))

                      .Select(k => k.Key);

        return changed.ToList();

    }

    private static object GetIfExists(Dictionary<string, object> values, string fieldName)

    {

        return values.ContainsKey(fieldName) ? values[fieldName] : null;

    }

    private static bool AreValueEquals(object o1, object o2)

    {

        return (o1 != null && o1.GetType().IsValueType)

            ? o1.Equals(o2)

            : o1 == o2;

    }

}