c# - Get "corners" of a 2d array

Question

I have a 2d array of nullable ints (try guessing what exactly it's for).
From that, I want to get both the first and last non-null elements from the first and last rows each.

How do I do this?

class Foo
{
    int?[,] array = new int?[3,9]
    {
        { null ,   13 , 21   , null , null ,   52 ,   69 , 76 , null },
        {    9 ,   15 , null ,   36 ,   45 , null , null , 77 , null },
        { null , null , null ,   39 ,   48 ,   53 , null , 79 ,   87 },
    };
}

Answer 1

From that, I want to get both the first and last non-null elements from the first and last rows each.

2D arrays are a pain in the ass, but they behave like one long array if you iterate them

var w = array.GetLength(1);
var h = array.GetLength(0);
var a = array.Cast<int?>();

var ff = a.First(e => e.HasValue);
var fl = a.Take(w).Last(e => e.HasValue);
var lf = a.Skip((h-1)*w).First(e => e.HasValue);
var ll = a.Last(e => e.HasValue);

Width is 9, Height is 3, Casting turns it into an enumerable of int? which means your corners are the first non null, the last non null in the initial 9, the first non null after skipping 18 and the last non null