How to access a specific element of a list by two keys without iterating through the list?

Question

C++ / C#

How to access a specific list element by two keys x, y without iterating through the list?
something like ListPixels.xy
without iterating over the list each time foreach

public class LPixels
{
   public static List<Pixels> ListPixels = new List<Pixels>();
}

public class Pixels
{
   public int x;
   public int y;
   public string text;
}

Answer 1

LINQ

class Program
{
  static void Main()
  {
    var lpixels = new LPixels();

    lpixels.ListPixels.Add(new Pixels(1, 1, "test11"));
    lpixels.ListPixels.Add(new Pixels(1, 2, "test12"));
    lpixels.ListPixels.Add(new Pixels(2, 1, "test21"));

    var find = lpixels.ListPixels.First(x => x.x == 1 && x.y == 2);

    Console.WriteLine(find.text);
  }
}

public class LPixels
{
  public List<Pixels> ListPixels = new List<Pixels>();
}

public class Pixels
{
  public Pixels (int x, int y, string text)
  {
    this.x = x;
    this.y = y;
    this.text = text;
  }

  public int x;
  public int y;
  public string text;
}

Answer 2

You can, but it's still a wrapper over the loop

//Один элемент
var result = ListPixels.SingleOrDefault(x=> x.x = someX && x.y = someY);
//Первый элемент
result = ListPixels.FirstOrDefault(x=> x.x = someX && x.y = someY);
//коллекция элементов
var results = ListPixels.Where(x=> x.x = someX && x.y = someY);

Answer 3

It is possible to be slightly perverted and to make an indexer. something like this

public class Pixel
{
  public int X {get;set}
  public int Y {get;set}
  public string Text {get;set}	
}

public class LPixels
{
  public List<Pixel> ListPixels = new List<Pixel>();
  
  public Pixel this[int x, int y]
  {
    get
    {
      return ListPixels.FirstOrDefault(px => px.X == x && px.Y == y);
    }
    set
    {
      var point = ListPixels.FirstOrDefault(px => px.X == x && px.Y == y);
      if(point != null)
      {
        point.Text = value.Text;
      }
      else
      {
        var newPoint = new Point
        {
          X = x;
          Y = y;
          Text = value.Text;
        }
        
        ListPixels.Add(newPoint);
      }			
    }
  }
}

var lpixels = new LPixels();
var result = lpixels[1, 2];
lpixels[1, 2] = new Point { Text = "Test" };

Answer 4

If you really need a quick search, then you should use hash tables, at least the same Dictionary.
It is enough to declare a class to public class Pixels : IEquatable<Pixels>declare methods:

public bool Equals(Pixels p)
{
    return x == p.x && y == p.y;
}
public override int GetHashCode()
{
    return x.GetHashCode() ^ y.GetHashCode();
}

And store not in a list, but in a dictionary. If order is also important, then OrderedDictionary can be used.