calculate the annual discharge over several years

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Maria Mateus 2013-10-29

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评论： Maria Mateus 2013-10-29

Hello,

I have a time series dataset that consists of daily discharge (Q) data from 1915-2006. My matrix: the first column is the year, the second is the month, the third is the day and the fourth column is the data of interest (Q). I need to calculate the mean annual discharge for each year and then arrange the data from the smallest Q to largest Q but knowing to which year that Q belongs.

Year Month day Q
1915 10 1 2.13E+02
1915 10 2 2.89E+02
1915 10 3 8.10E+02
...
...
2006 12 31 2.20E+04

I am very new at Matlab and even though I found some similar examples online I can't figure this out. Any help will be really appreciated.

Thanks!

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sixwwwwww 2013-10-29

编辑：sixwwwwww 2013-10-29

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Can you show sample for your data? Perhaps you can also look at:

doc mean

in your MATLAB command window and it will give you some idea

Jeremy 2013-10-29

Also look at the 'sort" function, specifically when called with 2 outputs.

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Answer 1

Cedric 2013-10-29

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编辑：Cedric 2013-10-29

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EDIT after you edited the question: it seems that there are 4 columns and not 2, and the discharge is in column4. I am updating my answer accordingly.

Here is an example

 data = [1915,  7,  1, 6; ...
         1915, 10,  3, 8; ...
         1915, 12,  8, 7; ...
         1916,  4, 22, 3; ...
         1916,  7, 13, 2] ;
 % - Get unique years and assign IDs starting at 1.
 years  = unique( data(:,1) ) ;
 yearId = data(:,1) - min( data(:,1) ) + 1 ;
 % - Compute Q mean per year.
 Qmean  = accumarray( yearId, data(:,4), [], @mean ) ;
 % - Sort Qmean and get corresponding years.
 [Qmean_sorted, ix] = sort( Qmean ) ;
 years_sorted = years(ix) ;

Running this, you get

 >> Qmean 
 Qmean =
        7.0000
        2.5000
 >> Qmean_sorted
 Qmean_sorted =
        2.5000
        7.0000
 >> years_sorted
 years_sorted =
        1916
        1915

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Maria Mateus 2013-10-29

Thank you so much. This works great!

Cedric 2013-10-29

You're welcome.

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Answer 2

sixwwwwww 2013-10-29

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Dear Maria, here is the code for required functionality:

ID = fopen('filename.txt');
data = textscan(ID, '%f%f%f%f');
fclose(ID);
year = data{1};
interest = data{4};
count = 1;
i = 1915:2006;
avg = zeros(length(i), 2);
for i = 1915:2006
    ind = find(ismember(year, i));
    avg(count, 1) = i;
    avg(count, 2) = sum(interest(ind)) / length(ind);
    count = count + 1;
end
avg = sortrows(avg, 2);
disp(avg)