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 int s. 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 AreDictionariesEqual it says DictionaryComparer<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);

Answer 2

I know this question already has an accepted answer, but I'd like to offer an even simpler alternative:

using System.Linq;
using System.Collections.Generic;

namespace Foo
{
    public static class DictionaryExtensionMethods
    {
        public static bool ContentEquals<TKey, TValue>(this Dictionary<TKey, TValue> dictionary, Dictionary<TKey, TValue> otherDictionary)
        {
            return (otherDictionary ?? new Dictionary<TKey, TValue>())
                .OrderBy(kvp => kvp.Key)
                .SequenceEqual((dictionary ?? new Dictionary<TKey, TValue>())
                                   .OrderBy(kvp => kvp.Key));
        }
    }
}

Answer 3

Convert the dictionary to a KeyValuePair list and then compare as collections:

CollectionAssert.AreEqual(
   dict1.OrderBy(kv => kv.Key).ToList(),
   dict2.OrderBy(kv => kv.Key).ToList()
);

Answer 4

I think that AreDictionariesEqual() just needs another method for List comparison

So if order of entries doesn't matter you can try this:

  static bool ListEquals(List<int> L1, List<int> L2)
{
    if (L1.Count != L2.Count)
        return false;

    return L1.Except(L2).Count() == 0;
}            
    /*
    if it is ok to change List content you may try
    L1.Sort();
    L2.Sort();
    return L1.SequenceEqual(L2);
    */


static bool DictEquals(Dictionary<string, List<int>> D1, Dictionary<string, List<int>> D2)
{
    if (D1.Count != D2.Count)
        return false;

    return D1.Keys.All(k => D2.ContainsKey(k) && ListEquals(D1[k],D2[k]));

}

And if order of entries matters, try this:

static bool DictEqualsOrderM(Dictionary<string, List<int>> D1, Dictionary<string, List<int>> D2)
{
    if (D1.Count != D2.Count)
        return false;

    //check keys for equality, than lists.           
    return (D1.Keys.SequenceEqual(D2.Keys) && D1.Keys.All(k => D1[k].SequenceEqual(D2[k])));         
}

Answer 5

The accepted answer above will not always return a correct comparison because using a HashSet to compare 2 lists will not account for duplicate values in the lists. For instance if the OP had:

var dict1 = new Dictionary<string, List<int>>() { { "A", new List<int>() { 1, 2, 1 } } };
var dict2 = new Dictionary<string, List<int>>() { { "A", new List<int>() { 2, 2, 1 } } };

Then the result of the dictionary comparison is they are equal, when they are not. The only solution I see is to sort the 2 list and compare the values by index, but I'm sure someone smarter then me can come up with a more efficient way.

Answer 6

If two dictionaries are known to use equivalent implementations of IEqualityComparer , and one wishes to regard as equivalent all keys which that implementation regardss as equivalent, they contain the same number of items, and one (arbitrarily chosen) maps all of the elements keys found in the other to corresponding values from the other, they will be equivalent unless or until one of them is modified. Testing for those conditions will be faster than any approach which does not not assume that both dictionaries use the same IEqualityComparer .

If two dictionaries do not use the same implementation of IEqualityComparer , they should generally not be considered equivalent regardless of the items they contain. For example, a Dictionary<String,String> with a case-sensitive comparer and one with a case-insensitive comparer, both of which contain the key-value pair ("Fred", "Quimby") are not equivalent, since the latter would map "FRED" to "Quimby", but the former would not.

Only if the dictionaries use the same implementation of IEqualityComparer , but if one is interested in a finer-grained definition of key-equality than the one used by the dictionaries and a copy of the key is not stored with each value, it will it be necessary to build a new dictionary for the purpose of testing the original dictionaries for equality. It may be best to delay this step until the earlier test has suggested that the dictionaries seem to match. Then build a Dictionary<TKey,TKey> which maps each key from one of the dictionaries to itself, and then look up all of the other dictionary's keys in that to make sure that they map to things which match. If both dictionaries used case-insensitive comparers, and one contained ("Fred", "Quimby") and the other ("FRED", "Quimby"), the new temporary dictionary would map "FRED" to "Fred", and comparing those two strings would reveal that the dictionaries don't match.

Answer 7

Here is a way using Linq, probably sacrificing some efficiency for tidy code. The other Linq example from jfren484 actually fails the DoesOrderValuesMatter() test, because it depends on the default Equals() for List<int> , which is order-dependent.

private bool AreDictionariesEqual(Dictionary<string, List<int>> dict1, Dictionary<string, List<int>> dict2)
{
    string dict1string = String.Join(",", dict1.OrderBy(kv => kv.Key).Select(kv => kv.Key + ":" + String.Join("|", kv.Value.OrderBy(v => v))));
    string dict2string = String.Join(",", dict2.OrderBy(kv => kv.Key).Select(kv => kv.Key + ":" + String.Join("|", kv.Value.OrderBy(v => v))));

    return dict1string.Equals(dict2string);
}

Answer 8

Most of the answers are iterating the dictionaries multiple times while it should be simple:

    static bool AreEqual(IDictionary<string, string> thisItems, IDictionary<string, string> otherItems)
    {
        if (thisItems.Count != otherItems.Count)
        {
            return false;
        }
        var thisKeys = thisItems.Keys;
        foreach (var key in thisKeys)
        {
            if (!(otherItems.TryGetValue(key, out var value) &&
                  string.Equals(thisItems[key], value, StringComparison.OrdinalIgnoreCase)))
            {
                return false;
            }
        }
        return true;
    }

Answer 9

I like this approach because it gives more details when the test fails

    public void AssertSameDictionary<TKey,TValue>(Dictionary<TKey,TValue> expected,Dictionary<TKey,TValue> actual)
    {
        string d1 = "expected";
        string d2 = "actual";
        Dictionary<TKey,TValue>.KeyCollection keys1= expected.Keys;
        Dictionary<TKey,TValue>.KeyCollection keys2= actual.Keys;
        if (actual.Keys.Count > expected.Keys.Count)
        {
            string tmp = d1;
            d1 = d2;
            d2 = tmp;
            Dictionary<TKey, TValue>.KeyCollection tmpkeys = keys1;
            keys1 = keys2;
            keys2 = tmpkeys;
        }

        foreach(TKey key in keys1)
        {
            Assert.IsTrue(keys2.Contains(key), $"key '{key}' of {d1} dict was not found in {d2}");
        }
        foreach (TKey key in expected.Keys)
        {
            //already ensured they both have the same keys
            Assert.AreEqual(expected[key], actual[key], $"for key '{key}'");
        }
    }

Answer 10

public static IDictionary<string, object> ToDictionary(this object source)
    {
        var fields = source.GetType().GetFields(
            BindingFlags.GetField |
            BindingFlags.Public |
            BindingFlags.Instance).ToDictionary
        (
            propInfo => propInfo.Name,
            propInfo => propInfo.GetValue(source) ?? string.Empty
        );

        var properties = source.GetType().GetProperties(
            BindingFlags.GetField |
            BindingFlags.GetProperty |
            BindingFlags.Public |
            BindingFlags.Instance).ToDictionary
        (
            propInfo => propInfo.Name,
            propInfo => propInfo.GetValue(source, null) ?? string.Empty
        );

        return fields.Concat(properties).ToDictionary(key => key.Key, value => value.Value); ;
    }
    public static bool EqualsByValue(this object source, object destination)
    {
        var firstDic = source.ToFlattenDictionary();
        var secondDic = destination.ToFlattenDictionary();
        if (firstDic.Count != secondDic.Count)
            return false;
        if (firstDic.Keys.Except(secondDic.Keys).Any())
            return false;
        if (secondDic.Keys.Except(firstDic.Keys).Any())
            return false;
        return firstDic.All(pair =>
          pair.Value.ToString().Equals(secondDic[pair.Key].ToString())
        );
    }
    public static bool IsAnonymousType(this object instance)
    {

        if (instance == null)
            return false;

        return instance.GetType().Namespace == null;
    }
    public static IDictionary<string, object> ToFlattenDictionary(this object source, string parentPropertyKey = null, IDictionary<string, object> parentPropertyValue = null)
    {
        var propsDic = parentPropertyValue ?? new Dictionary<string, object>();
        foreach (var item in source.ToDictionary())
        {
            var key = string.IsNullOrEmpty(parentPropertyKey) ? item.Key : $"{parentPropertyKey}.{item.Key}";
            if (item.Value.IsAnonymousType())
                return item.Value.ToFlattenDictionary(key, propsDic);
            else
                propsDic.Add(key, item.Value);
        }
        return propsDic;
    }

Answer 11

Comparing dictionary using string keys is way more complex than what it looks at first glance.

Dictionary<TKey,TValue> uses an IEqualityComparer<TKey> every time you access an entry in the dictionary to compare your input with the actual entries. The comparer is also used for hash calculations, which serves as some kind of index for faster random access to the entries. Trying to compare dictionaries with different comparers may have some side effects on key sorting and equality considerations for the key-value pair. The key point here is you need to compare the comparers too when comparing dictionaries.

Dictionary<TKey,TValue> also provides collections of keys and values, but they are unsorted. The keys and values collections are consistent inside the dictionary (the nth key is the nth value's key), but not across instances. This means we'll have to work with KeyValuePairs<TKey,TValue> and sort them by key on both dictionaries before comparing them.

However, the comparers in the dictionary only check for equality, it's not able to sort the keys. In order to sort pairs, we'll need a new IComparer<TKey> instance, which is another interface than IEqualityComparer<TKey> . But there's a trap here: default implementations of these two interfaces are not consistent. When you create a dictionary using the default contructor, the class will instanciate a GenericEqualityComparer<TKey> if TKey implements IEquatable<TKey> , which require TKey to implement bool Equals(TKey other); (otherwise, it will fallback to an ObjectEqualityComparer). If you create default Comparer, that will instanciate a GenericComparer<TKey> if TKey implements IComparable<TKey> , which will require TKey to implement int CompareTo(TKey other); (otherwise it will default to an ObjectComparer). Not all types implement both interfaces, and those who do sometimes use different implementations. There is a risk that two different keys (according to Equals) are sorted identically (according to CompareTo). In that case, there's a risk on the key sorting consitency.

Fortunately, string implements both interfaces. Unfortunately, its implementations are NOT consistent: CompareTo depends on the current culture to sort items, whereas Equals does not ! The solution to this problem is to inject a custom comparer to the dictionary, which provides consistent implementation of both interface. We can use StringComparer for that rather than relying on the default implementation. Then we'll simply get the dictionary comparer, cast it, and use it for sorting keys. Also, StringComparer allows comparing the comparers, so we can ensure both dictionaries use the same one.

First, we need a way to compare the values of the dictionary. Since you want to compare lists of int without order, we'll implement an generic equality comparer that sorts items and SequenceEqual them.

internal class OrderInsensitiveListComparer<TValue>
    : IEqualityComparer<IEnumerable<TValue>>
{
    private readonly IComparer<TValue> comparer;

    public OrderInsensitiveListComparer(IComparer<TValue> comparer = null)
    {
        this.comparer = comparer ?? Comparer<TValue>.Default;
    }

    public bool Equals([AllowNull] IEnumerable<TValue> x, [AllowNull] IEnumerable<TValue> y)
    {
        return x != null
            && y != null
            && Enumerable.SequenceEqual(
                x.OrderBy(value => value, comparer),
                y.OrderBy(value => value, comparer));
    }

    public int GetHashCode([DisallowNull] IEnumerable<TValue> obj)
    {
        return obj.Aggregate(17, (hash, item) => hash * 23 ^ item.GetHashCode());
    }
}

Now, we've got the values covered, but we also need to compare KeyValuePair . It is a simple ref struct, so we don't need to check for nulls. We'll simply delegate the comparison to two comparers : one for the key, another for the value.

internal class KeyValuePairComparer<TKey, TValue> : IEqualityComparer<KeyValuePair<TKey, TValue>>
{
    private readonly IEqualityComparer<TKey> key;

    private readonly IEqualityComparer<TValue> value;

    public KeyValuePairComparer(
        IEqualityComparer<TKey> key = null,
        IEqualityComparer<TValue> value = null)
    {
        this.key = key ?? EqualityComparer<TKey>.Default;
        this.value = value ?? EqualityComparer<TValue>.Default;
    }

    public bool Equals([AllowNull] KeyValuePair<TKey, TValue> x, [AllowNull] KeyValuePair<TKey, TValue> y)
    {
        // KeyValuePair is a struct, you can't null check
        return key.Equals(x.Key, y.Key) && value.Equals(x.Value, y.Value);
    }

    public int GetHashCode([DisallowNull] KeyValuePair<TKey, TValue> obj)
    {
        return 17 * 23 ^ obj.Key.GetHashCode() * 23 ^ obj.Value.GetHashCode();
    }
}

Now, we can implement the dictionary comparer. We do null check and compare the dictionaries comparers. Then we consider the dictionary as a simple enumerable of KeyValuePair and SequenceEqual them after sorting them by key. For that, we cast the dictionary comparer and delegate the comparison to the KeyValueComparer.

internal class DictionaryComparer<TValue> : IEqualityComparer<Dictionary<string, TValue>>
{
    private readonly IEqualityComparer<TValue> comparer;

    public DictionaryComparer(
        IEqualityComparer<TValue> comparer = null)
    {
        this.comparer = comparer ?? EqualityComparer<TValue>.Default;
    }

    public bool Equals([AllowNull] Dictionary<string, TValue> x, [AllowNull] Dictionary<string, TValue> y)
    {
        return x != null
            && y != null
            && Equals(x.Comparer, y.Comparer)
            && x.Comparer is StringComparer sorter
            && Enumerable.SequenceEqual(
                x.AsEnumerable().OrderBy(pair => pair.Key, sorter),
                y.AsEnumerable().OrderBy(pair => pair.Key, sorter),
                new KeyValuePairComparer<string, TValue>(x.Comparer, comparer));
    }

    public int GetHashCode([DisallowNull] Dictionary<string, TValue> obj)
    {
        return new OrderInsensitiveListComparer<KeyValuePair<string, TValue>>()
            .GetHashCode(obj.AsEnumerable()) * 23 ^ obj.Comparer.GetHashCode();
    }
}

Finally, we only need to instanciate comparers and let them do the work.

    private bool AreDictionariesEqual(Dictionary<string, List<int>> dict1, Dictionary<string, List<int>> dict2)
    {
        return new DictionaryComparer<List<int>>(
            new OrderInsensitiveListComparer<int>())
                .Equals(dict1, dict2);
    }

However, for this to work, we need to use a StringComparer in every dictionary.

    [TestMethod]
    public void DoesOrderValuesMatter()
    {
        Dictionary<string, List<int>> dict1 = new Dictionary<string, List<int>>(StringComparer.CurrentCulture);
        // more stuff
    }

Answer 12

The function shown below can be accommodated to perform any generic comparison:

public bool AreDictionaryEquals(Dictionary<ulong?, string> dictionaryList1, Dictionary<ulong?, string> dictionaryList2)
{

   if (dictionaryList1.Count != dictionaryList2.Count)
      return false;

   IDictionary<ulong?, string> orderedList1 = new Dictionary<ulong?, string>();
   IDictionary<ulong?, string> orderedList2 = new Dictionary<ulong?, string>();

   foreach (var itemDict1 in dictionaryList1.OrderByDescending(key => key.Id))
   {

     orderedList1.Add(itemDict1.Id, itemDict1.PropertyX);

   }

   foreach (var itemDict2 in dictionaryList2.OrderByDescending(key => key.Id))
   {

     orderedList2.Add(itemDict2.Id, itemDict2.PropertyX);

   }

  //check keys and values for equality
  return (orderedList1.Keys.SequenceEqual(orderedList2.Keys) && orderedList1.Keys.All(k => orderedList1[k].SequenceEqual(orderedList2[k])));

}

1- If the length of both dictionaries is not equal we can safely return false.

2- Then, we proceed to sort both dictionaries using the value of the keys. The reason for doing this is you could have situations like this:

Dictionary A: [1,A], [3,B]

Dictionary B: [3,B], [1,A]

Even though the order is not the same, the content of both can be considered equal.

Finally:

3- We compare both sorted sequences and retrieve the result of this comparison.