moncol = 3; %according to the header
prcpcol = 6;
monnums = untitled(1:95, moncol);
prcps = untitled(1:95, prcpcol);
monmax = accumarray(monnums(:), prcps(:), [], @max, NaN);
This code assumes that when you say that you want the maximum for each month, that you are saying that (e.g.) March 1963 should be considered to be the same group of data as (say) March 2008 -- you did not say maximum for each month within each year. If there does not happen to be any data for a particular month (over all of the years) then NaN will appear.
If you want the maximum for each month within each year, then:
moncol = 3; %according to the header
yearcol = 5;
prcpcol = 6;
monnums = untitled(1:95, moncol);
yearnums = untitled(1:95, yearcol);
prcps = untitled(1:95, prcpcol);
firstyear = min(yearnums);
idx = [yearnums(:) - firstyear + 1, monnums(:)];
monmax = accumarray(idx, prcps(:), [], @max, NaN);
The result will be a 2D array, with (row number plus firstyear) being the year it relates to, and the column number being the month number. If there does not happen to be any data for a particular year+month combination, then NaN will appear.
