Matlab IIR filter implementation
So this solution works: 

x = load('data.csv');
windowSize = 10; 
b = (1/windowSize)*ones(1,windowSize);
i = 1;

for n = windowSize: length(x)
    m = 0;
    tempSum = 0;
        for j = 1 : windowSize
            temp = b(j)*x(n-m);
            tempSum = tempSum + temp;
            m = m + 1;
        end
    y(i,:) = [tempSum]
    i = i+1;
end


See results below:





Instead of having really inaccurate results in the beginning I just skip these. It's important to note that you are losing an amount of samples equal to the number of b coefficients in this solution. So make sure to rescale the X-axis. 

Results were compared using Matlabs C = setdiff(y,yy) function and found no difference between the proposed solution and Matlabs filter(b,a,x) function.