MATLAB: Write loop for read then write multiple files

binaryfopenfor looplooploopsmultiple

Hi!

I've wrote a script for read a binary float32 file, then write it into a txt file. I works for one file, but i have several binary files. The file names are 001001.bin,001002.bin…etc.

Here is the original loop:

fname='D:\001001.bin';
fid = fopen(fname);
data = fread(fid,'float32');
dlmwrite('001001.bin.txt',data,'precision','%10.5f','newline','pc')

I tried to make a loop, but it has an error message: "In an assignment A(:) = B, the number of elements in A and B must be the same."

Here is the loop:

v=dir('*.bin')
for i=1001:v
fname(i)='D:\00(i).bin';
fid(i) = fopen(fname(i));
data(i) = fread(fid(i),'float32');
dlmwrite('00(i).bin.txt',data(i),'precision','%10.5f','newline','pc')
end

Thanks for helping!

Best Answer

This is not meaningful:

v=dir('*.bin')
for i=1001:v

dir replies a struct, which contains file names, dates, sizes and a flag, if it is a file or folder. Then 1001:v is not an option.

fname(i)='D:\00(i).bin';

This tries to assign the char vector 'D:\00(i).bin' to the scalar element fname(i). But this cannot work, because you cannot store a vector in a scalar. In addition "(i)" is not, what you want, but you want to replace the "i" by a number. Use sprintf for this.

data(i) = fread(fid(i),'float32');

Again a vector is assigned to a scalar.

See https://www.mathworks.com/matlabcentral/answers/57446-faq-how-can-i-process-a-sequence-of-files.

Folder   = cd;  % Better define this explicitly
FileList = dir(fullfile(Folder, '*.bin'));
for iFile = 1:length(FileList)
  FileIn = fullfile(Folder, FileList(iFile).name);
  [fid, msg] = fopen(FileIn);
  if fid == -1
    error('Cannot open file: %s', FileIn);
  end
  data = fread(fid, 'float32');
  fclose(fid);  % Close the file - important!
    FileOut = [FileIn, '.txt'];
    dlmwrite(FileOut, data, 'precision', '%10.5f', 'newline', 'pc');
  end

By the way: Text files are a bad option for storing numerical data. The limited precision reduces the accuracy, the conversion to numbers is expensive, the files are larger and the advantage of text files does not matter here: that a human can edit the file.

Instead of taking the file names from dir, you can create them also:

for iFile = 1001:1000 + numel(FileList)
  File = fullfile(Folder, sprintf('%.6d.bin', iFile));
  ...

The '%.6d' format specifier inserts leading zeros such that the output has 6 digits.

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 a = dir('d:\mytimsarehere\*.tim');
 for i = 1:numel(a)
  filename_in = ['d:\mytimsarehere\' a(i).name];
  filename_out = [filename_in(1:end-3) 'txt'];
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Ali - how do you know that your images are in the correct order? For example, what does

 Files = dir('*.jpg');

return? I'm going to guess that your file names have a number in them, but you may not be getting the order that you expect. For example, the following loop creates a 100 (empty) text files

 for k=1:100
      fid = fopen(sprintf('test%d.txt',k),'wt');
      fclose(fid);
 end

Now when I do

 dir('test*.txt')

I observe that

               test18.txt   test28.txt   test38.txt   test48.txt   test58.txt   test68.txt   test78.txt   test88.txt   test98.txt   
  test1.txt    test19.txt   test29.txt   test39.txt   test49.txt   test59.txt   test69.txt   test79.txt   test89.txt   test99.txt   
  test10.txt   test2.txt    test3.txt    test4.txt    test5.txt    test6.txt    test7.txt    test8.txt    test9.txt    
  test100.txt  test20.txt   test30.txt   test40.txt   test50.txt   test60.txt   test70.txt   test80.txt   test90.txt   
  test11.txt   test21.txt   test31.txt   test41.txt   test51.txt   test61.txt   test71.txt   test81.txt   test91.txt   
  test12.txt   test22.txt   test32.txt   test42.txt   test52.txt   test62.txt   test72.txt   test82.txt   test92.txt   
  test13.txt   test23.txt   test33.txt   test43.txt   test53.txt   test63.txt   test73.txt   test83.txt   test93.txt   
  test14.txt   test24.txt   test34.txt   test44.txt   test54.txt   test64.txt   test74.txt   test84.txt   test94.txt   
  test15.txt   test25.txt   test35.txt   test45.txt   test55.txt   test65.txt   test75.txt   test85.txt   test95.txt   
  test16.txt   test26.txt   test36.txt   test46.txt   test56.txt   test66.txt   test76.txt   test86.txt   test96.txt   
  test17.txt   test27.txt   test37.txt   test47.txt   test57.txt   test67.txt   test77.txt   test87.txt   test97.txt

Note the ordering of the files: 1,10,100,11-19,2,20-29,3,30-39,etc. with early images being inserted every ten images. If your files are named in a similar fashion then you will need to force the correct order or rename he files. If, in the code above, I had named the files as

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      fclose(fid);
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where each integer is padded with up to three zeros, then I get the correct ordering of the files as

dir('test*.txt')
test001.txt  test012.txt  test023.txt  test034.txt  test045.txt  test056.txt  test067.txt  test078.txt  test089.txt  test100.txt  
test002.txt  test013.txt  test024.txt  test035.txt  test046.txt  test057.txt  test068.txt  test079.txt  test090.txt  
test003.txt  test014.txt  test025.txt  test036.txt  test047.txt  test058.txt  test069.txt  test080.txt  test091.txt  
test004.txt  test015.txt  test026.txt  test037.txt  test048.txt  test059.txt  test070.txt  test081.txt  test092.txt  
test005.txt  test016.txt  test027.txt  test038.txt  test049.txt  test060.txt  test071.txt  test082.txt  test093.txt  
test006.txt  test017.txt  test028.txt  test039.txt  test050.txt  test061.txt  test072.txt  test083.txt  test094.txt  
test007.txt  test018.txt  test029.txt  test040.txt  test051.txt  test062.txt  test073.txt  test084.txt  test095.txt  
test008.txt  test019.txt  test030.txt  test041.txt  test052.txt  test063.txt  test074.txt  test085.txt  test096.txt  
test009.txt  test020.txt  test031.txt  test042.txt  test053.txt  test064.txt  test075.txt  test086.txt  test097.txt  
test010.txt  test021.txt  test032.txt  test043.txt  test054.txt  test065.txt  test076.txt  test087.txt  test098.txt  
test011.txt  test022.txt  test033.txt  test044.txt  test055.txt  test066.txt  test077.txt  test088.txt  test099.txt

Best Answer

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