C# Compare two dictionaries for equality

Question

I want to compare in C# two dictionaries with as keys a string and as value a list of ints. I assume two dictionaries to be equal when they both have the same keys and for each key as value a list with the same integers (both not necessarily in the same order).

I use both the answers from this and this related question, but both fail my test suite for the test functions DoesOrderKeysMatter and DoesOrderValuesMatter.

My test suite:

using System; using Microsoft.VisualStudio.TestTools.UnitTesting; using System.Collections.Generic; using System.Linq;   namespace UnitTestProject1 {     [TestClass]     public class ProvideReportTests     {         [TestMethod]         public void AreSameDictionariesEqual()         {             // arrange             Dictionary<string, List<int>> dict1 = new Dictionary<string, List<int>>();             List<int> list1 = new List<int>();             list1.Add(1);             list1.Add(2);             dict1.Add("a", list1);             List<int> list2 = new List<int>();             list2.Add(3);             list2.Add(4);             dict1.Add("b", list2);              // act             bool dictsAreEqual = false;             dictsAreEqual = AreDictionariesEqual(dict1, dict1);              // assert             Assert.IsTrue(dictsAreEqual, "Dictionaries are not equal");          }          [TestMethod]         public void AreDifferentDictionariesNotEqual()         {             // arrange             Dictionary<string, List<int>> dict1 = new Dictionary<string, List<int>>();             List<int> list1 = new List<int>();             list1.Add(1);             list1.Add(2);             dict1.Add("a", list1);             List<int> list2 = new List<int>();             list2.Add(3);             list2.Add(4);             dict1.Add("b", list2);              Dictionary<string, List<int>> dict2 = new Dictionary<string, List<int>>();              // act             bool dictsAreEqual = true;             dictsAreEqual = AreDictionariesEqual(dict1, dict2);              // assert             Assert.IsFalse(dictsAreEqual, "Dictionaries are equal");          }          [TestMethod]         public void DoesOrderKeysMatter()         {             // arrange             Dictionary<string, List<int>> dict1 = new Dictionary<string, List<int>>();             List<int> list1 = new List<int>();             list1.Add(1);             list1.Add(2);             dict1.Add("a", list1);             List<int> list2 = new List<int>();             list2.Add(3);             list2.Add(4);             dict1.Add("b", list2);              Dictionary<string, List<int>> dict2 = new Dictionary<string, List<int>>();             List<int> list3 = new List<int>();             list3.Add(3);             list3.Add(4);             dict2.Add("b", list3);             List<int> list4 = new List<int>();             list4.Add(1);             list4.Add(2);             dict2.Add("a", list4);              // act             bool dictsAreEqual = false;             dictsAreEqual = AreDictionariesEqual(dict1, dict2);              // assert             Assert.IsTrue(dictsAreEqual, "Dictionaries are not equal");          }          [TestMethod]         public void DoesOrderValuesMatter()         {             // arrange             Dictionary<string, List<int>> dict1 = new Dictionary<string, List<int>>();             List<int> list1 = new List<int>();             list1.Add(1);             list1.Add(2);             dict1.Add("a", list1);             List<int> list2 = new List<int>();             list2.Add(3);             list2.Add(4);             dict1.Add("b", list2);              Dictionary<string, List<int>> dict2 = new Dictionary<string, List<int>>();             List<int> list3 = new List<int>();             list3.Add(2);             list3.Add(1);             dict2.Add("a", list3);             List<int> list4 = new List<int>();             list4.Add(4);             list4.Add(3);             dict2.Add("b", list4);              // act             bool dictsAreEqual = false;             dictsAreEqual = AreDictionariesEqual(dict1, dict2);              // assert             Assert.IsTrue(dictsAreEqual, "Dictionaries are not equal");          }           private bool AreDictionariesEqual(Dictionary<string, List<int>> dict1, Dictionary<string, List<int>> dict2)         {             return dict1.Keys.Count == dict2.Keys.Count &&                    dict1.Keys.All(k => dict2.ContainsKey(k) && object.Equals(dict2[k], dict1[k]));              // also fails:             //    return dict1.OrderBy(kvp => kvp.Key).SequenceEqual(dict2.OrderBy(kvp => kvp.Key));         }     } } 

What is the correct way to compare these kind of dictionaries? Or is there an error in my (admittedly clumsily written) TestSuite?

Update

I'm trying to incorporate Servy's answer in my test suite, like below, but I get some errors (underlined with a red wiggly line in Visual Studio):

• SetEquals in the `Equals method says: "does not contain a definition for SetEquals accepting a first argument of type Generic.List.

• In AreDictionariesEqualit saysDictionaryComparer<List> is a type but is used as a variable.`

  namespace UnitTestProject1 {     [TestClass]     public class ProvideReportTests     {         [TestMethod]         // ... same as above            private bool AreDictionariesEqual(Dictionary<string, List<int>> dict1, Dictionary<string, List<int>> dict2)         {             DictionaryComparer<string, List<int>>(new ListComparer<int>() dc = new DictionaryComparer<string, List<int>>(new ListComparer<int>();             return dc.Equals(dict1, dict2);          }      }      public class DictionaryComparer<TKey, TValue> :         IEqualityComparer<Dictionary<TKey, TValue>>     {         private IEqualityComparer<TValue> valueComparer;         public DictionaryComparer(IEqualityComparer<TValue> valueComparer = null)         {             this.valueComparer = valueComparer ?? EqualityComparer<TValue>.Default;         }         public bool Equals(Dictionary<TKey, TValue> x, Dictionary<TKey, TValue> y)         {             if (x.Count != y.Count)                 return false;             if (x.Keys.Except(y.Keys).Any())                 return false;             if (y.Keys.Except(x.Keys).Any())                 return false;             foreach (var pair in x)                 if (!valueComparer.Equals(pair.Value, y[pair.Key]))                     return false;             return true;         }          public int GetHashCode(Dictionary<TKey, TValue> obj)         {             throw new NotImplementedException();         }     }      public class ListComparer<T> : IEqualityComparer<List<T>>     {         private IEqualityComparer<T> valueComparer;         public ListComparer(IEqualityComparer<T> valueComparer = null)         {             this.valueComparer = valueComparer ?? EqualityComparer<T>.Default;         }          public bool Equals(List<T> x, List<T> y)         {             return x.SetEquals(y, valueComparer);         }          public int GetHashCode(List<T> obj)         {             throw new NotImplementedException();         }     }      public static bool SetEquals<T>(this IEnumerable<T> first, IEnumerable<T> second, IEqualityComparer<T> comparer)         {             return new HashSet<T>(second, comparer ?? EqualityComparer<T>.Default)                 .SetEquals(first);         }  } 

Answer 1

So first we need an equality comparer for dictionaries. It needs to ensure that they have matching keys and, if they do, compare the values of each key:

public class DictionaryComparer<TKey, TValue> :     IEqualityComparer<Dictionary<TKey, TValue>> {     private IEqualityComparer<TValue> valueComparer;     public DictionaryComparer(IEqualityComparer<TValue> valueComparer = null)     {         this.valueComparer = valueComparer ?? EqualityComparer<TValue>.Default;     }     public bool Equals(Dictionary<TKey, TValue> x, Dictionary<TKey, TValue> y)     {         if (x.Count != y.Count)             return false;         if (x.Keys.Except(y.Keys).Any())             return false;         if (y.Keys.Except(x.Keys).Any())             return false;         foreach (var pair in x)             if (!valueComparer.Equals(pair.Value, y[pair.Key]))                 return false;         return true;     }      public int GetHashCode(Dictionary<TKey, TValue> obj)     {         throw new NotImplementedException();     } } 

but this isn't enough on its own. We need to compare the values of the dictionary using another custom comparer, not the default comparer as the default list comparer won't look at the values of the list:

public class ListComparer<T> : IEqualityComparer<List<T>> {     private IEqualityComparer<T> valueComparer;     public ListComparer(IEqualityComparer<T> valueComparer = null)     {         this.valueComparer = valueComparer ?? EqualityComparer<T>.Default;     }      public bool Equals(List<T> x, List<T> y)     {         return x.SetEquals(y, valueComparer);     }      public int GetHashCode(List<T> obj)     {         throw new NotImplementedException();     } } 

Which uses the following extension method:

public static bool SetEquals<T>(this IEnumerable<T> first, IEnumerable<T> second,     IEqualityComparer<T> comparer) {     return new HashSet<T>(second, comparer ?? EqualityComparer<T>.Default)         .SetEquals(first); } 

Now we can simply write:

new DictionaryComparer<string, List<int>>(new ListComparer<int>())     .Equals(dict1, dict2);