Testing for equality between dictionaries in c#

Question

Assuming dictionary keys and values have their equals and hash methods implemented correctly, what is the most succinct and efficient way to test for equality of two dictionaries?

In this context two dictionaries are said to be equal if they contain the same set of keys (order not important), and for every such key, they agree on the value.

here are some ways i came up with (there are probably many more):

public bool Compare1<TKey, TValue>(
    Dictionary<TKey, TValue> dic1, 
    Dictionary<TKey,TValue> dic2)
{
    return dic1.OrderBy(x => x.Key).
        SequenceEqual(dic2.OrderBy(x => x.Key));
}

public bool Compare2<TKey, TValue>(
    Dictionary<TKey, TValue> dic1, 
    Dictionary<TKey, TValue> dic2)
{
    return (dic1.Count == dic2.Count && 
        dic1.Intersect(dic2).Count().
        Equals(dic1.Count));
}

public bool Compare3<TKey, TValue>(
    Dictionary<TKey, TValue> dic1, 
    Dictionary<TKey, TValue> dic2)
{
    return (dic1.Intersect(dic2).Count().
        Equals(dic1.Union(dic2).Count()));
}

Answer 1

It really depends on what you mean by equality.

This method will test that two dictionaries contain the same keys with the same values (assuming that both dictionaries use the same IEqualityComparer<TKey> implementation).

public bool CompareX<TKey, TValue>(
    Dictionary<TKey, TValue> dict1, Dictionary<TKey, TValue> dict2)
{
    if (dict1 == dict2) return true;
    if ((dict1 == null) || (dict2 == null)) return false;
    if (dict1.Count != dict2.Count) return false;

    var comparer = EqualityComparer<TValue>.Default;

    foreach (KeyValuePair<TKey, TValue> kvp in dict1)
    {
        TValue value2;
        if (!dict2.TryGetValue(kvp.Key, out value2)) return false;
        if (!comparer.Equals(kvp.Value, value2)) return false;
    }
    return true;
}

Answer 2

dic1.Count == dic2.Count && !dic1.Except(dic2).Any();

Answer 3

You could use linq for the key/value comparisons:

public bool Compare<TKey, TValue>(Dictionary<TKey, TValue> dict1, Dictionary<TKey, TValue dict2)
{
    IEqualityComparer<TValue> valueComparer = EqualityComparer<TValue>.Default;

    return  dict1.Count == dict2.Count &&
            dict1.Keys.All(key => dict2.ContainsKey(key) && valueComparer.Equals(dict1[key], dict2[key]));
}

Answer 4

@Allen's answer:

bool equals = a.Intersect(b).Count() == a.Union(b).Count()

is about arrays but as far as IEnumerable<T> methods are used, it can be used for Dictionary<K,V> too.

Answer 5

If two dictionaries contain the same keys, but in different order, should they be considered equal? If not, then the dictionaries should be compared by running enumerators through both simultaneously. This will probably be faster than enumerating through one dictionary and looking up each element in the other. If you have advance knowledge that equal dictionaries will have their elements in the same order, such a double-enumeration is probably the way to go.