Finding average

[femibode]

I would appreciate if anyone can help me. I'm struggling to write equation to compute average of a set that has more than one dimensions. E.g how do I find average of
X(i,j)
Y(i,j,k)

Thanks

[femibode]

I managed with the following but would like to know if there's other means as I need to find median as well
aveX = sum([i,j], X(i,j)) / (card(i)*card(j));
aveY = sum([i,j,k], Y(i,j,k)) / (card(i)*card(j)*card(k));