Question

I have observed daily data that I need to compare to generated Monthly data so I need to get a mean of each month over the thirty year period.

My observed data set is currently in 365×31 with rows being each day (no leap years!) and the extra column being the month number (1-12).

the problem I am having is that I can only seem to get a script to get the mean of all years. ie. I cannot figure how to get the script to do it for each column separately. Example of the data is below:

1    12    14
1    -15   10
2    13    3
2    2     37
...all the way to 12 for 365 rows

SO: to recap, I need to get the mean of [12; -15; 13; 2] then [14; 10; 3; 37] and so on.

I have been trying to use the unique() function to loop through which works for getting the number rows to average but incorrect means. Now I need it to do each month(28-31 rows) and column individually. Result should be a 12×30 matrix. I feel like I am missing something SIMPLE. Code:

u = unique(m); %get unique values of m (months) ie) 1-12

for i=1:length(u)
   month(i) = mean(obatm(u(i), (2:31)); % the average for each month of each year
end

Appreciate any ideas! Thanks!

Answer 1

You can simply filter the rows for each month and then apply mean, like so:

month = zeros(12, size(obatm, 2));
for k = 1:12
    month(k, :) = mean(obatm(obatm(:, 1) == k, :));
end

EDIT:
If you want something fancy, you can also do this:

cols = size(obatm, 2) - 1;
subs = bsxfun(@plus, obatm(:, 1), (0:12:12 * (cols - 1)));
vals = obatm(:, 2:end);
month = reshape(accumarray(subs(:), vals(:), [12 * cols, 1], @mean), 12, cols)

Look, Ma, no loops!