Error using fprintf. Function is not defined for 'struct' inputs.

I'm reading all the DICOM files in a directory. I'm supposed to run 1 file after the other for K-NN classification. So, I run a loop, and individually classify the files for which I've used the for loop.

dicomFiles = dir('*.dcm');
for k = 1:(numfiles)
I=dicomread(strcat(location, '\', dicomFiles(k).name));

This is where I've called knnclassify() and when I use disp(xclass), it results in either of the groups i.e, 'Yes' or 'No'.

xclass = knnclassify(SM, B, G, VK, METH, RULE, KF);

I'm supposed to write the result of the classification into a file with the format -

   Name       Group
  C1.dcm       Yes
  N1.dcm       No

So, I've used the following code to write the contents into a file.

   %Output KNN results to a file
          op_dir = 'F:\8th sem Project\Code\KNN Result';
          if exist(strcat(op_dir,'\KNN_Result.dat'),'file')
          delete(strcat(op_dir,'\KNN_Result.dat'));
          end

          op = strcat(op_dir,'\KNN_Result.dat');
          fid3 = fopen(op, 'a+');
          fprintf(fid3, '%s %s \n', dicomFiles(k), xclass);

However, I get an error saying - Error using fprintf. Function is not defined for 'struct' inputs. I've tried going through all the posts on the internet regarding the same, but if I change it to dicomFiles{k}, there are different errors. I'm not used to with the syntax of Matlab. Please help!

[Greg]

Your answer is on line 3 of the first block of your own supplied code.

[prahlad h]

Could you please elaborate? I know dicomFiles is a Nx1 struct array with fields:

    name
    date
    bytes
    isdir
    datenum

The only thing I want to write into the file, is the name, of each file, which is why maybe dicomFiles(k, 1) would work, but it doesn't.

Also, xclass seems to be a struct too.

[Stephen23]

 dicomFiles(k).name

As Greg told you, this already is used on line three.

[prahlad h]

Goodness..what a dumb moment. I wasted hours on this haha. Thanks so much.

[Walter Roberson]

http://www.mathworks.co.uk/matlabcentral/answers/43073-a-guide-to-tags

Answer 1

[Jan]

At first the code can be simplified:

   %Output KNN results to a file - 
   % !!! open it ONCE BEFORE the loop over k!!!
   file = fullfile('F:\8th sem Project\Code\KNN Result\KNN_Result.dat';
   fid3 = fopen(op, 'w');  % Deletes formerly existing file automatically
   if fid3 == -1, error('Cannot open file for writing: %s', file); end

Now the actual problem: The message means, that one of the arguments is a struct. Here it is at least "dicomFiles", which has been created by dir(). If the output should be the name (you did not explain this):

   fprintf(fid3, '%s %s \n', dicomFiles(k).name, xclass);

Now I'm not sure, what the class of xlcass is. If it is really a string, the shown code will work.

Don't forget to close the file after the loop:

fclose(fid3)

[prahlad h]

I was writing each time the loop was running. That wasn't a problem. Thanks for the answer though, it did work, stupidity on my part.

fprintf(fid3, '%s %s \n', dicomFiles(k).name, xclass);

^wouldn't work now because apparently xclass is a cell - Error using fprintf Function is not defined for 'cell' inputs.

If you have an answer for this, then great. Else, I'd just compare the value of xclass to the groups and write the output to 2 separate files.

Thank you!