MATLAB: Open a txt file written with dlmwrite

dlmwritefopenfopen -1read txt fiiles

I've written a rather large txt file using the dlmwrite() function. Now I'm trying to open the file and read it so I can plot the data. I'm getting an error trying to use fopen(). I've looked through the documentation for fopen() and found that it returns -1, which means it's unable to open it, but it's not clear why. I'm able to open the file fine with excel or notepad. What are some reasons that fopen will fail?

Best Answer

I was able to solve the problem by opening it with write access like so:

fileID = fopen('Test2014Data3.txt','w');

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MATLAB: Trying to delete lines that start with an alphabet on a text file

Use fopen, fgetl, fclose to read your file into a cell array and discard the lines you don't want. Or if you want to write a new file, use fopen, fprintf, fclose and write as your read:

fidi = fopen('somefile.txt', 'rt');
fido = fopen('newfile.txt', 'wt');
tline = fgetl(fidi);
while ischar(tline)
  if ~isempty(tline) && tline(1) >= '0' && tline(1) <= '9'
    %line to keep
    fprintf(fido, '%s\n', tline);
  end
  tline = fgetl(fidi);
end
fclose(fidi);
fclose(fido);

edit: forgot to read the next line!

MATLAB: Dlmwrite help

On systems that are not running MS Windows, and on MS Windows systems that do not have Excel installed, xlswrite() is restricted to "basic" mode, which can only handle numeric arrays.

To use dlmwrite() to write text, you have to do as I wrote before:

by submitting an array of pure characters and using a character format in the Precision parameter and setting the delimiter to be empty.

That would look like

dlmwrite(YourFilename, YourCharacterArray, 'delimiter', '', 'precision', '%c')

where YourCharacterArray is already fully converted to characters.

Referring to your earlier posting in which you had F, a column of words, and G, a column of numbers, that would be like

nrows = size(G,1);
YourCharacterArray = [repmat('"', nrows, 1), F, repmat('",',nrows,1), num2str(G)];

The above includes quoting the words and putting in the comma delimiter between the words and the numbers.

But if you are going to go through all this trouble to prepare everything as character ahead of time, all you have gained is incomprehensibility and slowness of your code, and all you have removed is one explicit file open and close. Better, likely, to use the low-level I/O operations recommended in the user guide

fid = fopen(YourFileName, 'wt');
for K = 1 : size(G,1)
  fprintf(fid, '"%s",%f\n', F(K,:), G(K));
end
fclose(fid)

That is 5 easy lines that nearly any programmer will understand, compared to 3 lines for the dlmwrite() that relatively few people will understand (and those who do understand them will wonder why you didn't just use fprintf() !)

Going the dlmwrite() route is possible, but will cause more confusion than it solves problems. The only reason I had for inventing the technique a few years back was that other people said that it couldn't be done.

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