How can I get the sum (average) value of three lists in C#?

Question

I have three lists which each list represents only 0s and 1s which related to the pixel values of three images. My question is how can I get the sum (average) of those three lists and represent it in a new list? here is example of my image1:

List<int> image1 = new List<int>();
        int blackColor = 0;

        for (int x = 0; x < bmp1.Width; x++)
        {
            for (int y = 0; y < bmp1.Height; y++)
            {
                Color color = bmp1.GetPixel(x, y);

                if (color.ToArgb() == Color.Black.ToArgb())
                {
                    image1.Add(0);
                    blackColor++;                        
                }
                else
                {
                    image1.Add(1);
                }
            }
        }

Answer 1

Let me makes sure I understand the problem. You have three lists of the same length:

list A:  1, 2, 4, 3
list B:  3, 2, 4, 1
List C:  2, 7, 1, 8

and you wish to get a third list that is the average of each:

List D:  2, 4, 3, 4

Yes?

This is a job for zip join.

var sumOfFirstTwo = list1.Zip(list2, (x, y)=>x + y);

sumOfFirstTwo is now the sequence that is the sum of the first two lists.

var sumOfAllThree = sumOfFirstTwo.Zip(list3, (x, y)=>x + y);

sumOfAllThree is now the sequence that is the sum of all three lists.

var average = sumOfAllThree.Select(x=>x/3).ToList();

Make sense?

Answer 2

This works for an arbitrary number of lists

var firstList = new[] { 1, 2, 3, 1 };
var secondList = new[] { 2, 3, 1, 1 };
var thirdList = new[] { 3, 1, 2, 2 };
var lists = new[] { firstList, secondList, thirdList };

var listLengths = lists.Select(x => x.Count());
if (listLengths.Distinct().Count() != 1)
    throw new Exception("Line lengths must be the same");
var lengthOfEachList = listLengths.First();
var averages = new List<double>();
for (var i = 0; i != lengthOfEachList; ++i) {
    averages.Add(lists.Average(x => x[i]));
}

The LINQ way would be

var averages = Enumerable.Range(0, lengthOfEachList).Select(x => lists.Average(y => y[x]));