Calculate mean monthly from daily values

I have a file that is 22281 rows x 5 col. This represents 60 years of daily values. I need to calculate mean monthly values for all years and extract, say, only May, to a new file. The resulting output will be 60 values for mean monthly data for May. This will be to compare col4 to col5 (below).

col1=year
col2=month
col3=day
col4=data1
col5=data2

Please help!

Answer 1

[the cyclist]

Take a look at the solutions to this question: http://www.mathworks.com/matlabcentral/answers/27088-sort-data-by-day-of-year. You might find some ideas there that help you.

Answer 2

[Kostas]

maybe smt like this could work

suppose you have a matrix called data(22281,5) months are stored in second column

for i=1:12 %loop over months
idx=find(data(:,2)==i); % find all indeces for the specific month
meandata1=mean(idx,4);
meandata2=mean(idx,5);
meandata(i,:)=[i meandata1 meandata2]; %store in a new matrix the mean values per months
end

now you can just find and print in a file the values for the 5th month (May)

[Brandi Newton]

There might be an error in this code? I'm not an expert, but i think in the third line you're asking the program to take the mean of the idx variable, in the 4th dimension: meandata1=mean(idx,4).

Instead you should ask the program to take the mean of the "data" variable, at the row indexes indicated by idx, with column specified, and in the 1st dimension (columns, 2nd dimension is rows).

So:

for i=1:1 %loop over months
   idx=find(data(:,2)==i); % find all indeces for the specific month
   meandata1=mean(data(idx,4),1); %CHANGES HERE, assuming data is in column 4
   meandata(i,:)=[i meandata1]; %store in a new matrix the mean values per month
end

Does that make sense? It seems to be working for me now.

Thanks!

[Brandi Newton]

oh hang on, the code i wrote averages all days in all januaries. I need it for each year...

[per isakson]

See averaging over a timeseries

[Faisal Amri]

I Tried to modify, this what I got and it works for me though I still working to make it better. Hope this helps

k=1
  %Calculating Monthly Average
  for j=1992:2012                                     %Years Looping
      for i=1:12                                      %Months Looping
          idx=find((Data(:,1)==i) & (Data(:,3)==j));  %Find all indeces for the specific month
          meandata1=mean(Data(idx,4),1);
          Monthly_Ave(k,:)=[i,j,meandata1;];          %Store in a new matrix the mean values per month
          k=k+1;
      end
  end

[frankovaT]

Unfortunately this is not working either