尝试使用的除 LINQ扩展方法，该方法只能从第一列表中的项目，即不存在于第二个。例子如下：

 列表<串GT; ThirdList = SecondList.Except（FirstList）.ToList（）; 
 

您可以使用下面的代码打印结果：

  Console.WriteLine（的string.join（Environment.NewLine，ThirdList））; 
 

或

 的Debug.WriteLine（的string.join（Environment.NewLine，ThirdList））; 
 

请注意：不要忘记包括：使用System.Diagnostics程序;

打印：

  COM3 
 

I'am trying to check the difference between two List<string> in c#.

Example:

List<string> FirstList = new List<string>();
List<string> SecondList = new List<string>();

The FirstList is filled with the following values:

FirstList.Add("COM1");
FirstList.Add("COM2");

The SecondList is filled with the following values:

SecondList.Add("COM1");
SecondList.Add("COM2");
SecondList.Add("COM3");

Now I want to check if some values in the SecondList are equal to values in the FirstList.

If there are equal values like: COM1 and COM2, that are in both lists, then filter them from the list, and add the remaining values to another list.

So if I would create a new ThirdList, it will be filled with "COM3" only, because the other values are duplicates.

How can I create such a check?

Try to use Except LINQ extension method, which takes items only from the first list, that are not present in the second. Example is given below:

List<string> ThirdList =  SecondList.Except(FirstList).ToList();

You can print the result using the following code:

Console.WriteLine(string.Join(Environment.NewLine, ThirdList));

Or

Debug.WriteLine(string.Join(Environment.NewLine, ThirdList));

Note: Don't forget to include: using System.Diagnostics;

prints:

COM3