You cannot add a column to a text file by opening it with 'a' (append) access. You must re-write the entire text file to have everything it had before as well as the new column.
However, if all of the data files have the same number of columns, it is easier to read all the data in first and then to write it out in one step.
[Code revised to make it much more robust]
magiclen = 6625;
magiccol = 5;
n ='average.txt';
files = dir('*.txt');
%the file average.txt might have been detected by dir() so remove it
tf = arrayfun(@(K) strcmp(n, files(K).name), 1:length(files));
files(tf) = [];
nfile = length(files);
if nfile == 0
error('There were no files found');
end
if nfile == 1;
warning(sprintf('Only one file found, only one column of output expected: %s', files(1).name);
end
Lat = zeros(magiclen, nfile)
for F = 1:nfile
thisfile = files(F).name;
try
f = load(thisfile);
catch me
%if there was a load problem, say so
error(sprintf('Failed loading file %s', thisfile));
end
if any(size(f) < [magiclen,magiccol])
error(sprintf('File %s loaded but is too small, only (%d by %d) but need (%d+ by %d+)', thisfile, size(f,1), size(f,2), magiclen, magiccol));
end
Lat(1:magiclen,F) = f(1:magiclen, magiccol);
end
fmt = ['\n' repmat('%15.6f', 1, nfile) '\n'];
fid = fopen(n, 'wt')
fprintf(fid, fmt, Lat.' ); %the .' is important!
fclose(fid);
Note the complete lack of a loop in writing out the data after it has all been read in.
Computing the format and using .' on the array to write out are tricks of the trade -- things that are not obvious until you have worked with MATLAB enough that suddenly they are obvious.
