averaging files with different dates

hi! I have files from 1978 to 2009 every 10 days, named as follows:

1978_11.txt

1978_21.txt

. . .

2009_361.txt

2009_365.txt

I would like to average the day 11 of every year and generate a file, then the day 21 and so on, but I dont know how.

I know how to read the files (they are in the same folder, but not how to read the ones I know for the average... Can someone help me please?

thank you for your time

Answer 1

[Thorsten]

years = 1978:2009

for y = years

    pattern = sprintf('*_%d.txt', y);
    d = dir(pattern);

    Nfiles = numel(d);
    average = 0;
    for i = 1:numel(d)
       filename = d(i).name;

       % read data from filename
       % insert your function here

       % assume that the data is read into variable 'data'
       average = average + 1/Nfiles*data;
    end
    average_filename = sprintf('avg_%d.txt', y);
    % write data to file, e.g., using dlmwrite
    dlmwrite(average_filename, average)
  end

[Maite M.]

thank you it is what I need :)