Calculating variance in loop

Hi, I have 8 years of data and I want to calculate the variance of the same month but different year all together. i.e. Variance of January for all the 8 years. My matrix is 74*115*22168. I know there is the function var, but I'm finding problems to incorporate everything in a loop that does everything in one run. Any help pls

[dpb]

How do you have the dates available?

[Walter Roberson]

How does the 74*115*22168 matrix correspond to date? None of those values appear to divide nicely by 8 or "nearly" 365, so you do not appear to have data divided by day or by hour (or, say, 3 hours). Perhaps it is financial data only for business days: if so then to group it properly would require the date/time information.

[Image Analyst]

What does each row, column, and z-level of your 3-D matrix represent? Which index is time and what units is it? Can you get it into a shape where you have 12 so that each row or plane corresponds to a month?