Writing file in matlab with fprintf and dlmwrite in loop.

I'm trying to get a loop to write headers between matrices to a .txt file from matlab.

Example code:

filename = 'sampleXLS.dat';
datfile = fopen(filename,'w');

header = 'Header \n';
mat1 = [1,2,3;4,5,6]; 
mat2 = [7,8;9,10];
mat3 = [11;12;13];

mats = {mat1,mat2,mat3};
for iter = 1:length(mats)
   data = mats{iter}
   fprintf(datfile, header);
   dlmwrite(filename, data,'-append','delimiter',' ','precision', '%f');
end

I want

Header
1 2 3
4 5 6 
Header
7 8
9 10
Header 
11
12
13

I am getting

Header
Header
Header
 3
4 5 6 
7 8
9 10
11
12
13

Note the missing 1 and 2, when I step though the file in debug mode it is inserting and replacing the numbers with the headers as it goes along.

Is there a way to tell fprintf to append?

Answer 1

[Geoff Hayes]

The problem is using the fprintf and dlmwrite together - each behaves differently when writing data to file. See fprintf and dlmwrite for details and examples on their use.

The above code should use the same functions to write the text and numeric data to file. For example, dlmwrite can be used to write matrix to ASCII-delimited file. A text string is still a one-dimensional matrix and so can be written to file using this function (I know the documentation states that only numeric data can be written, but it is possible to write out a string). Just replace

fprintf(datfile, header);

with

 dlmwrite(filename,header,'-append','delimiter','');

where

 header = 'Header';

(without the new line character).

Else, replace the

 dlmwrite(filename, data,'-append','delimiter',' ','precision', '%f');

with

 for u=1:size(data,1)
     for v=1:size(data,2)
         fprintf(datfile,'%f ',data(u,v));
     end
     fprintf(datfile,'\n');
 end

Try either of the above and see what happens!

[Devon]

Thank you very much! Both options worked! I timed both and apparently the double loop ran faster than the dlmwrite.

[Geoff Hayes]

Glad it helped. Interesting timing results which may be due to each dlmwrite call opening and closing the file.