按公共元素匹配和加入列表

Question

The Situation is: I have a huge number of lists with a fixed size of 3 elements, for a group of four of those lists, there will be 4 unique elements that make up these lists. Example:

Elements = [Object A, Object B, Object C, Object D, Object E, Object F, Object G, Object H]
Lists:
List 1 = {A,B,C}
List 2 = {B,C,D}
List 3 = {C,D,A}
List 4 = {D,A,B}
List 5 = {E,F,G}
List 6 = {F,G,H}
List 7 = {G,H,E}
List 8 = {H,E,F}

So, in this example elements [A, B, C, D] made four lists of three elements per list. Here comes the question: how can I match these four lists to get a single list that Contains [A, B, C, D]

Edit: The Actual problem is: I have a list of 2D Lines, and I want to know every 4 lines that make a rectangle. I started with intersecting the lines, and I got a group of lists, each list contains a line that intersects with 2 more lines. Now the goal is to join these lists that have the four edges of the Rectangle.

Answer 1

Using modular arithmetic and sum will work. If you divide the index of the item by 4 and sum the 3 values you will be able to group by this number.

    class Program
    {
 
        static void Main(string[] args)
        {
            List<string> Elements = new List<string>() {"A","B","C","D","E","F","G","H"};
            MyClass[][] lists = {
                                  new MyClass[] {new MyClass() { name = "A", value = 0},new MyClass() { name = "B", value = 0},new MyClass() { name = "C", value = 0}},
                                  new MyClass[] {new MyClass() { name = "B", value = 0},new MyClass() { name = "C", value = 0},new MyClass() { name = "D", value = 0}},
                                  new MyClass[] {new MyClass() { name = "C", value = 0},new MyClass() { name = "D", value = 0},new MyClass() { name = "A", value = 0}},
                                  new MyClass[] {new MyClass() { name = "D", value = 0},new MyClass() { name = "A", value = 0},new MyClass() { name = "B", value = 0}},
                                  new MyClass[] {new MyClass() { name = "E", value = 0},new MyClass() { name = "F", value = 0},new MyClass() { name = "G", value = 0}},
                                  new MyClass[] {new MyClass() { name = "F", value = 0},new MyClass() { name = "G", value = 0},new MyClass() { name = "H", value = 0}},
                                  new MyClass[] {new MyClass() { name = "G", value = 0},new MyClass() { name = "H", value = 0},new MyClass() { name = "E", value = 0}},
                                  new MyClass[] {new MyClass() { name = "H", value = 0},new MyClass() { name = "E", value = 0},new MyClass() { name = "F", value = 0}},
                              };

            var results = lists.Select(x => new { sum = (x.Select(y => Elements.IndexOf(y.name)/4).Sum()), values = x })
                .GroupBy(x => x.sum)
                .ToList();
        }
    }
    public class MyClass
    {
        public string name { get; set; }
        public int value { get; set; }
    }

Answer 2

I think your best bet would be to make use of a hashset :

HashSet<Letter> uniqueValues = new HashSet<Letter>();

Letter A = new Letter() { Name = "A" } ;
Letter B = new Letter() { Name = "B" };
Letter C = new Letter() { Name = "C" };
Letter D = new Letter() { Name = "D" };

Letter[] list1 = new Letter[] { A, B, C };
Letter[] list2 = new Letter[] { B, C, D };
Letter[] list3 = new Letter[] { C, D, A };
Letter[] list4 = new Letter[] { D, A, B };

var lists = new Letter[][] { list1, list2, list3, list4 };

foreach (var list in lists)
{
    foreach (var letter in list)
    {
        uniqueValues.Add(letter);
    }
}

Debug.WriteLine(string.Join(", ", uniqueValues));  //  A, B, C, D

Hashsets specifically don't record duplicate values, so no matter how many times you add the letter A to your hashset, it'll only appear once. That seems to be exactly what you're looking for.