data appending in text file

Question

Mohammad 2013-8-14

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Hi,

I created a text file using MATLAB. For example, 10 by 3 matrix and I saved it as a text using fopen and fprint in particular format. Now I want to append lines (data)to this text, say at row 1, row 5, and row 10, i.e at a fixed interval. How can I do this. Remember, I need to add lots of these lines.

I greatly appreciate any help.

Thanks Rafiq

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Answer 1

Cedric 2013-8-14

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编辑：Cedric 2013-8-14

Instead of opening the file with write permission using 'w', open it in with append permission using 'a'.

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Mohammad 2013-8-14

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Dear Cedric, Thank you very much for your response. It looks like I am getting something but not exactly the way I want. I added few lines with your code so that you can see what I want.

B=ones(10,3); fid=fopen('spot.txt','w'); spotformat='%8.3f%8.3f%8.3f\r\n'; fprintf(fid,spotformat, B); fclose(fid);

%So I made a file spot.txt with all entry one using B

data2insert = [3 4 5 6; 7 8 9 10; 11 12 13 14] ;

%I want this data2insert in the spot.txt. In the first line I want to insert 3 4 5 6, in the fifth line, I want to insert 7 8 9 10 and in the tenth line, I want to insert 11 12 13 14.

 atLine    = [1, 5, 10] ;
 lineCnt   = 1 ;
 insertCnt = 1 ;
 fid_in    = fopen('spot.txt', 'r') ;
 fid_out   = fopen('data.txt', 'w') ;
 while ~feof(fid_in)
    if lineCnt == atLine(insertCnt)
       fprintf(fid_out, '%f %f %f %f\r\n', data2insert(insertCnt,:)) 
       insertCnt = insertCnt + 1 ;
    end
    line = fgetl(fid_in);
    fwrite(fid_out, line) ;
    lineCnt = lineCnt + 1  ;
 end
 fclose(fid_in) ;
  while insertCnt < length(atLine)
     fprintf(fid_out, '%f %f %f %f\r\n', data2insert(insertCnt,:)) ;
     insertCnt = insertCnt + 1 ;
  end
  fclose(fid_out) ;

It looks like everything is coming out but only in three rows. It should be 13 lines (rows) in total. Your help is highly appreciated.

Thanks Rafiq

Mohammad 2013-8-15

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Dear Cedric, Thank you very much for your help. I was able to find the way I want it. I am struggling with few other things. If I increase B ==ones(15,3) and save it as spot.txt (my original text file), it looks like the output text is not reading after eleventh line. I am sorry for my naive questions. I tried to get it around. Also, MATLAB shows boundary limit problem. Could you please look at this. Thanks.

_B=ones(15,3);
fid=fopen('spot.txt','w');
fprintf(fid, '  Ek      SigE     SigX   SigY    SigAng VDSX   VDSY    \n');
spotformat='%8.3f%8.3f%8.3f\r\n';
fprintf(fid,spotformat, B);
fclose(fid);
data2insert = [3 4 5 6 7 8 9 10; 11 12 13 14 15 16 17 18;...
              19 20 21 22 23 24 25 26] ;
 atLine    = [2, 6, 10] ;
 lineCnt   = 1 ;
 insertCnt =1 ;
 fid_in    = fopen('spot.txt', 'r') ;
 fid_out   = fopen('data.txt', 'w') ;
   while ~feof(fid_in)
      if lineCnt == atLine(insertCnt)
         fprintf(fid_out, '%8.3f%8.3f%8.3f%8.3f%8.3f%8.3f%8.3f%8.3f\r\n',...
             data2insert(insertCnt,:)) ;
         insertCnt = insertCnt+1
      end
       line = fgetl(fid_in);
      fprintf(fid_out, '%s\r\n', line)
       lineCnt = lineCnt + 1  
   end
   fclose(fid_in) ;
    while insertCnt < length(atLine)
       fprintf(fid_out, '%8.3f%8.3f%8.3f%8.3f%8.3f%8.3f%8.3f%8.3f\r\n',...
           data2insert(insertCnt,:)) ;
       insertCnt = insertCnt + 1 ;
    end
    fclose(fid_out) ;_

Mohammad 2013-8-15

Cedric,

So kind of you. Thanks a lot. This solved my problem and saved me a lot of time. Thanks again.

Rafiq

Cedric 2013-8-15

You're welcome!

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Answer 2

Walter Roberson 2013-8-14

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https://ww2.mathworks.cn/matlabcentral/answers/84753-data-appending-in-text-file#answer_94292

The only way to insert lines into a text file is to read in the file and write out the modified file. There is no way to seek directly to a particular line, and there is no way to insert in the middle of a text file.

Depending on what you want to insert into the file, you may wish to use system utilities such as "sed" or "awk" or "perl"