Question

I’m having a List of String like

List<string> MyList = new List<string>
{ 
    "A-B", 
    "B-A", 
    "C-D", 
    "C-E", 
    "D-C",
    "D-E",
    "E-C",
    "E-D",
    "F-G",
    "G-F"
};

I need to remove duplicate from the List i.e, if “A-B” and “B-A” exist then i need to keep only “A-B” (First entry)

So the result will be like

"A-B"   
"C-D"
"C-E"   
"D-E"
"F-G"

Is there any way to do this using LINQ?

Answer 1

This returns the sequence you look for:

var result = MyList
    .Select(s => s.Split('-').OrderBy(s1 => s1))
    .Select(a => string.Join("-", a.ToArray()))
    .Distinct();

foreach (var str in result)
{
    Console.WriteLine(str);
}

In short: split each string on the - character into two-element arrays. Sort each array, and join them back together. Then you can simply use Distinct to get the unique values.

Update: when thinking a bit more, I realized that you can easily remove one of the Select calls:

var result = MyList
    .Select(s => string.Join("-", s.Split('-').OrderBy(s1 => s1).ToArray()))
    .Distinct();

Disclaimer: this solution will always keep the value “A-B” over “B-A”, regardless of the order in which the appear in the original sequence.