how to compare an array to see how many times does the elements repeats themself?

Question

I have a string array that contains a list every string in that list contains 4 initials, I want to compare how many times the initials repeat themselves

If the initials are repeated I want to add those initials to a List<string> and count how many times the initial repeat using a List<int>

• If ENFE appears in the array add that to List<string> and List<int> counts = 1

• If ENFE appears again counts = 2

• If CCOM appears add to List<string> and List<int> counts = 1....

This is the code i have

 foreach(string item in lstProgramas.Items)
        {
            
            if(tempDeptSiglas[1] == item)
            {
                deptSiglas.Add(tempDeptSiglas[1]);
                contador.Add(+1);
            }
        }

I'm getting that tempDeptSiglas is null

Answer 1

Attempting to answer "Some question" without fully understanding your problem.

In the below code - the Dictionary "should" contain counts for each Initials.

 List<string> initials = new List<string>();
 // Some way to fill initials collection
 List<string> searchInThis = new List<string>();
 // Some way to fill searchInThis collection
 Dictionary<string, int> initialCounts = new Dictionary<string, int>();

 searchInThis.ForEach(t =>
 {
    initials.ForEach(i =>
    {
       if(System.Text.RegularExpressions.Regex.IsMatch(t, i))
       {
          if (initialCounts.TryGetValue(i, out int count))
          {
             count++;
             initialCounts[i] = count;
          }
          else
          {
             initialCounts[i] = 1;
          }
       }
    });
 });

Obvisouly this can be optimized - with domain knowledge like if one Initial matches - we dont need to test other intials (duh..!!) and other stuff.