C＃比较字典是否相等

Posted 2021-04-10

如何最有效地比较两个字典的平等？ - 除了强力迭代的键，尝试查找和比较值

var d1 = new Dictionary<string,int>();
d1.Add("a",2);
d1.Add("b",1);
d1.Add("c",1);

var d2 = new Dictionary<string,int>();
d2.Add("c",1);
d2.Add("b",1);
d2.Add("a",2);

如何最有效地比较平等？

不像这样的暴力：

static bool CompareDictionaries(Dictionary<string,int> d1, Dictionary<string,int> d2)
{
    if (d1.Count != d2.Count) return false;
    foreach(string key in d1.Keys)
    {
        if (!d2.ContainsKey(key)) return false;
        if (d1[key] != d2[key]) return false;
    }
    return true;
}

答案

如果Dictionary键相同，则可以使用HashSet进行比较：

var set1 = new HashSet<int>(dictionary1.Values);
var set2 = new HashSet<int>(dictionary2.Values);

然后可以使用Union，Intersect，HopsSet公开的除外。此外，您可以使用此：

bool isEqual = set1.SetEquals(set2);

根据您的情况，基准测试是（HashSet vs Dictionary）here

另一答案

结合自定义SequenceEquals扩展，您可以指定如何比较键和值，如下所示：

public static bool Equals<TKey, TValue>(IDictionary<TKey, TValue> a, IDictionary<TKey, TValue> b,
    IComparer<TKey> keyComparer, IEqualityComparer<TValue> valueComparer)
{
    if (ReferenceEquals(a, b))
        return true;

    if (b == null || a == null)
        return false;

    if (a.Count != b.Count)
        return false;

    var aOrdered = a.OrderBy(k => k.Key, keyComparer);
    var bOrdered = b.OrderBy(k => k.Key, keyComparer);

    return aOrdered.SequenceEqual(bOrdered, valueComparer);
}

延期：

public static bool SequenceEqual<TKey, TValue>(this IEnumerable<KeyValuePair<TKey, TValue>> first, IEnumerable<KeyValuePair<TKey, TValue>> second, IEqualityComparer<TValue> valueComparer)
{
    if (valueComparer == null) valueComparer = EqualityComparer<TValue>.Default;
    if (first == null) throw new ArgumentNullException(nameof(first));
    if (second == null) throw new ArgumentNullException(nameof(second));

    using (IEnumerator<KeyValuePair<TKey, TValue>> e1 = first.GetEnumerator())
    using (IEnumerator<KeyValuePair<TKey, TValue>> e2 = second.GetEnumerator())
    {
        while (e1.MoveNext())
        {
            if (!(e2.MoveNext() && valueComparer.Equals(e1.Current.Value, e2.Current.Value))) return false;
        }
        if (e2.MoveNext()) return false;
    }
    return true;
}

您可以在OP的特定Dictionary<string,int>示例中调用它：

var areEqual = Equals(d1, d2, StringComparer.OrdinalIgnoreCase, EqualityComparer<int>.Default);