cumsum function for seperate time

Hi

I have 2 data colomn. 1-colomn time in a form(01/01/1975, 05/01/1975, 25/01/1975, 05/02/1975,...., 22/11/2015), second colomn constant values corresponding to the time(75, 25, 30, 70,..., 55). I wanted to calculate monthly cumulative sum values.Such as for 1-month sum value should appear as 130(75+25+30). And sequences continue...

How I may do it?

Thanks!

Answer 1

[Are Mjaavatten]

Interesting problem. Here is one possible solution:

 dates = {'01/01/1975'; '05/01/1975'; '25/01/1975'; '05/02/1975';...
     '15/02/1975';'12/03/1975';'17/02/1978'};
 data = [75;25;30;70;32;24;49];

 time = datenum(dates,'dd/mm/yyyy');  % Convert strings to Matlab dates
 [Y,M] = datevec(time);               % Extract year and month vectors
 mnthno = Y*12+M;                     % Unique value for every month
 [C,ia] = unique(mnthno);             % List of unique months
 sums = zeros(size(C));               % Allocate space for the sums 
 for i = 1:length(C)
     sums(i) = sum(data(mnthno==C(i)));  % Sum data for each month
     % Display results:
     fprintf('Year: %4d, Month = %2d, sum = %6.2f \n',...
         Y(ia(i)),M(ia(i)), sums(i));
 end

You should type

 doc datenum
 doc datevec
 doc unique

if you are not sure what the different functions do.