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CSharp · Console

/Program.cs

using System;
using System.Collections;
using System.Collections.Generic;

namespace Demo
{
    public static class Program
    {
        public static void Main()
        {
            var matrix = new string[5, 10];

            for (int row = 0; row < matrix.GetLength(0); ++row)
            {
                for (int col = 0; col < matrix.GetLength(1); ++col)
                {
                    matrix[row, col] = $"{row}, {col}";
                }
            }

            var col3 = new ArrayColumn<string>(matrix, column: 3); // Grab column 3

            for (int col = 0; col < col3.Count;  ++col)
            {
                Console.WriteLine(col3[col]);
            }

            Console.WriteLine("-----------------");

            foreach (var element in col3)
            {
                Console.WriteLine(element);
            }
        }
    }        

    public sealed class ArrayColumn<T>: IReadOnlyList<T>
    {
        public ArrayColumn(T[,] matrix, int column)
        {
            _matrix = matrix;
            _column = column;
            Count   = _matrix.GetLength(0);
        }

        public IEnumerator<T> GetEnumerator()
        {
            IEnumerable<T> items()
            {
                for (int row = 0; row < Count; ++row)
                {
                    yield return _matrix[row, _column];
                }
            }

            return items().GetEnumerator();
        }

        IEnumerator IEnumerable.GetEnumerator()
        {
            return GetEnumerator();
        }

        public int Count { get; }

        public T this[int index] => _matrix[index, _column];

        readonly T[,] _matrix;
        readonly int  _column;
    }
}