How to find the common string from list of strings in C#

Question

I have a Dictionary as below
Dictionary<string, List<Structure>> myDic = new Dictionary<string, List<Structure>>();

string[] tests = new string[] { "test", "test2", "test3", "test4" };

foreach (string test in tests)
{
myDic.Add(value, new List<Structure>{ });
}

struct Structure
{
string name1;
string name2;
}

I have a foreach loop which is as mentioned below

foreach (KeyValuePair<string, List<Structure>> pair in myDictionary)
{
string key = pair.Key;
Console.WriteLine("The output Key is: " + key);
foreach (Structure item in pair.Value)
{
string value = item.name2;
Console.WriteLine("The output value is: " + value);
}
}

THE OUTPUT OF THIS FOR_EACH GOES LIKE BELOW:
The key prints test1, test2, test3, test4 as outputs // (foreach KeyValuePair<string, list<structure="">> pair in myDictionary)

and the value prints
A for test1 iteration
A, B for test2 iteration
A, C, D for test3 iteration
A, C, F for test4 iteration

Now since A is common for all the tests (which is test1, test2, test3 and test4)

I need my output over as
"The output key is: test1, the output value is A"
"The output key is: test2, the output value is A"
"The output key is: test3, the output value is A"
"The output key is: test4, the output value is A"

/////////////////////////////////////////////////////////////////////////////////////////////////////////////

If there is no common value for all the Keys(test1, test2, test3 and test4), then I need to throw an exception

That is, if the
The Key is: test1
The value is: A

The Key is: test2
The value is: B

The Key is: test3
The value is: C

The Key is: test4
The value is: D

In this case since, there is no common value in for all the Keys, I need to throw an exception

/////////////////////////////////////////////////////////////////////////////////////////////////////////////

If there is 3 common values for keys (i.e., as mentioned below)
The Key is: test1
The value is: A
The value is: B

The Key is: test2
The value is: A
The value is: B
The value is: C

The Key is: test3
The value is: C
The value is: A

The Key is: test4
The value is: D

In this case, the output needs to be
The key is: test1 and the value is: A
The key is: test2 and the value is: A
The key is: test3 and the value is: A
The key is: test4 and the value is: D

Answer 1

@UserName123 , Welcome to Microsoft Q&A, you could try the following code to get what you wanted.

 Dictionary<string, List<Structure>> myDic = new Dictionary<string, List<Structure>>();  
  
        string[] tests = new string[] { "test1", "test2", "test3", "test4" };  
  
        foreach (string test in tests)  
        {  
            myDic.Add(test, new List<Structure> { });  
  
        }  
        myDic["test1"].Add(new Structure { name1 = "A" });  
        myDic["test1"].Add(new Structure { name1 = "B" });  
        myDic["test2"].Add(new Structure { name1 = "A" });  
        myDic["test2"].Add(new Structure { name1 = "B" });  
        myDic["test2"].Add(new Structure { name1 = "C" });  
        myDic["test3"].Add(new Structure { name1 = "C" });  
        myDic["test3"].Add(new Structure { name1 = "A" });  
        myDic["test4"].Add(new Structure { name1 = "D" });  
        List<List<string>> all=new List<List<string>>();  
        var result=myDic.Select(x => x.Value.Distinct());  
        foreach (KeyValuePair<string, List<Structure>> pair in myDic)  
        {  
            List<string> list = new List<string>();  
            foreach (Structure item in pair.Value)  
            {  
                string value = item.name1;  
   
                list.Add(value);  
            }  
            all.Add(list);  
        }  
        var comm= all.SelectMany(x => x).Distinct()  
              .Where(x => all.Select(y => (y.Contains(x) ? 1 : 0))  
              .Sum() >=3).ToList();  
        foreach (KeyValuePair<string, List<Structure>> pair in myDic)  
        {  
            string key = pair.Key;  
            Console.WriteLine("The output Key is: " + key);  
            if(comm.Count()==0)  
            {  
                Console.WriteLine("throw the exception");  
            }  
            else  
            {  
                if(pair.Value.Select(i=>i.name1).Intersect(comm).Any())  
                {  
                    foreach (var item in comm)  
                    {  
                        Console.WriteLine("The output value is: " + item);  
                    }  
                }  
                else  
                {  
                    foreach (var item in pair.Value)  
                    {  
                        Console.WriteLine("The output value is: " + item.name1);  
                    }  
                }  
                  
            }  
        }  

I tested the above three conditions, they all work well.

The final condition result:

Best regards,
Jack

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