How to generate a string in my code with more easier way in C#

It's splitting according to underscores at the end it removes first and last two items.

Well, while this is a correct describtion, its not precise enough.

The code splits a string and then removes all occurences of the first and last two items. E.g.

namespace ConsoleCS
{
    using System;
    using System.Linq;

    public class Program
    {
        public static void Main(string[] args)
        {
            string test = "a_b_c_d_e_a_b_c";
            Console.WriteLine(GetCutForceChannelBaseName(test));

            Console.WriteLine("\nDone.");
            Console.ReadLine();
        }

        public static string GetCutForceChannelBaseName(string fullname)
        {
            string[] parseFullName = fullname.Split(new string[] { "_" }, StringSplitOptions.None);
            parseFullName = parseFullName.Where(w => w != parseFullName[Array.IndexOf(parseFullName, parseFullName.First())]).ToArray();
            parseFullName = parseFullName.Where(w => w != parseFullName[Array.IndexOf(parseFullName, parseFullName.Last())]).ToArray();
            parseFullName = parseFullName.Where(w => w != parseFullName[Array.IndexOf(parseFullName, parseFullName.Last())]).ToArray();
            string generateName = string.Join("_", parseFullName);
            return generateName;
        }
    }
}

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returns d_e. But as First and Last are defined on the mutating intermediate result, this means especially Last is not a fixed value. E.g. using

string test = "a_b_c_d_e_a_b_c_a";

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returns also d_e.

Thus the question is imho wrong. It's not about efficiency. The question is:

What is the correct logic?

Yes for removing two last items first i remove last and then read that one and again remove last one so at the end i can be able to remove last two one. Yes you're right it's more about logic.
 
parseFullName = parseFullName.Where(w => w != parseFullName[Array.IndexOf(parseFullName, parseFullName.Last())]).ToArray();
parseFullName = parseFullName.Where(w => w != parseFullName[Array.IndexOf(parseFullName, parseFullName.Last())]).ToArray();

Please confirm that you want the following output for the given samples:

a_b_c_d_e_a_b_c             => d_e
a_b_c_d_e_a_b_c_a           => d_e
a_b_c_d_e_a_b_c_a_a_a_a_a   => d_e
a_b_c_d_e_a_aaaaa_b_c_aaaaa => b_d_e_b
a_b_c_d_e_f_a_b             => c_d_e

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The keyword is "all occurances".

Hi ste5an,

it's currently doing that:

string test = "a_b_c_d_e_f_g_h";

array = a, b, c, d, e, f, g, h

//Remove first
a, b, c, d, e, f, g, h => b, c, d, e, f, g, h

// Remove last
b, c, d, e, f, g, h  => b, c, d, e, f, g

// Again remove last
b, c, d, e, f, g => b, c, d, e, f


Join with "_"
b_c_d_e_f

and b_c_d_e_f is my target string.

@saige, that's exactly the reason why I asked for the logic.. Cause yours implements #1 whereas the original code implements #3.

@ste5an, understood.  I thought about trying to comment additionally pointing out what you were stating, but your comments were pretty clear to me.  ;)

-saige-