write data to specific column in text file

I have this text file created from

I = imread('3.jpg');
i = im2bw(I);
m = max(max(i));
[r c] = find(i == m);
fid = fopen('lalit.txt','wt');
for j=1:length(r)
fprintf(fid,'%f %f\n',r(j),c(j));
end
fclose(fid);
 Now i want to do 
for m = 1:length(r)
z(m) = round((r(m) + c(m))/2);
end
z=z';

Now i want to save this z as third column in the same text file, but without modifying r and c.

Answer 1

[Walter Roberson]

The only way you should seriously consider for modifying data in text files is to read in the file and write the modified version to another file, possibly followed by renaming the new file to the old name. Modifying a text file "in place" is tricky and often not possible anyhow.

[Lalit Patil]

clear all; clc; I = imread('1.jpg'); i = im2bw(I); imshow(i); m = max(max(i)); [r c] = find(i == m); a = r; fid = fopen('lalit.txt','wt'); for j=1:length(r) fprintf(fid,'%f %f\n',r(j),c(j)); end fclose(fid);

data = textread('lalit.txt'); a = unique(data); for i=a', maxVal = max(data(a==i,2)); minVal = min(data(a==i,2)); z(i,:) = round((maxVal + minVal)/2); end

fid = fopen('lalit1.txt','wt'); for j=1:length(z) fprintf(fid,'%f\n',z(j)); end fclose(fid);

Thank you.. I got it.. it doesn't matter for me whethere i write data to same file or another file..