MATLAB: How can i convert daily rainfall data in monthly data

data convertmonthlytimetable

I have daily rainfall data of 113 year of 17415 station in 41273*129*135; format where 41273 is days and 129*135 no of stations. Data is in .mat format.

Best Answer

I suggest reorganizing your data into a timetable with 41273 rows and 4 columns: Time, Lat, Long, RainFall.
Then you can use retime() to perform monthly operations such as sum, mean, etc.
Here's an example. 
% Create fake data
dt = datetime('01/Jan/1900') : datetime('31/Dec/2012'); 
long = randi(360,size(dt))-180; 
lat =  randi(180,size(dt))-90; 
rainfall = rand(size(dt))*10; 
% Put data into timetable
tt = timetable(dt',lat',long',rainfall','VariableNames',{'Lat','Long','Rainfall'});
% Calculate monthly rainfall combining all locations
monthlyRainfall = retime(tt,'Monthly','Sum');
See the link I provided to retime() for many other ways to use this function with timetables.
[Update]
To convert your 3D array to a time table, follow this demo. This demo uses 1000 days of fake data rather than 41273 days which would take a lot of time to generate the random numbers. There are two different ways to represent your 17415 locations and both ways are included in the code - you choose which is best. 
% Here's a fake version of your data except for 1000 days (to save processing time). 
% With the size of your data, some of these lines could consume some significant time.
% The vectors must be column vectors. 
data = rand(1000, 129, 135); 
dt = datetime('01/Jan/1900') + (0:999)'; %column vector of 1000 dates

loc1 = (1:129)'; %Column vector
loc2 = (1:135)'; %Column vector 
% Create the columns for the table.  Each of these vars should be same size.
dataVec = data(:); 
dtVec = repmat(dt,size(data,2)*size(data,3),1); 
loc1Vec = repmat(repelem(loc1,size(data,1)),size(data,3),1); 
loc2Vec = repelem(loc2,size(data,1)*size(data,2),1); 
% Create time table
tt = timetable(dtVec,loc1Vec,loc2Vec,dataVec,'VariableNames',{'Lat','Long','Rainfall'});
% --OR--
[~,~,locGroups] = unique([loc1Vec,loc2Vec],'rows'); 
tt = timetable(dtVec,locGroups,dataVec,'VariableNames',{'LocationGroup','Rainfall'});
% Look at first 10 rows
tt(1:10,:)
[Update II]
If you'd like to perform operations for each month AND for each location, you should organize your timetable so that each location gets its own column. 
data = rand(90, 129, 135); 
dt = datetime('01/Jan/1900') + (0:89)'; %column vector of 1000 dates
rainMat = reshape(data,size(data,1),[]); 
locNames = strsplit(sprintf('Loc%d ',1:size(rainMat,2))); 
tt = array2timetable(rainMat,'RowTimes',dt,'VariableNames', locNames(1:end-1)); 
moSum = retime(tt,'Monthly','Sum'); 
%View the first 2 months, first 6 locations
moSum(1:2,1:6)
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