使用LINQ的两个Dictionary<int，string>上的左外连接

Dictionary<int, string> dict1 = new Dictionary<int, string>();
dict1.Add(1, "Apple");
dict1.Add(2, "Banana");
dict1.Add(3, "Orange");

Dictionary<int, string> dict2 = new Dictionary<int, string>();
dict2.Add(1, "Red");
dict2.Add(2, "Yellow");
dict2.Add(4, "Green");

var result = from d1 in dict1
             join d2 in dict2 on d1.Key equals d2.Key into joined
             from j in joined.DefaultIfEmpty()
             select new { Key = d1.Key, Value1 = d1.Value, Value2 = j?.Value };

foreach (var item in result)
{
    Console.WriteLine($"Key: {item.Key}, Value1: {item.Value1}, Value2: {item.Value2}");
}

Key: 1, Value1: Apple, Value2: Red
Key: 2, Value1: Banana, Value2: Yellow
Key: 3, Value1: Orange, Value2: