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From: Jan Simon on 19 Jan 2010 14:20
Dear Hadassa!

> I have a large file of about 2000 rows and many more columns.

Do you want to sort each row, all rows together or the sequence of rows?

> I want to sort the rows in this file according to a new index I have created.

Is this index a part of the rows or do you have it separately?

> That is, I actually do not care about the format of the values or the values
> when I read in the file. I would just like to read it in, sort it and write it back
> into the same file.

So what you need is a tool to read a file to a cell string with each line in a cell?
This would be:
C = dataread('file', FileName, '%s', 'delimiter', '\n', 'whitespace', '');
Then write the cell in sorted order:
FID = fopen(FileName, 'wt');
fprintf(FID, '%s\n', C{SortIndex});
fclose(FID);

If speed is critical and the file is really large, you coud try to use this:
FID = fopen(FileName, 'wt');
fwrite(FID, cat(1, C{SortIndex}), 'uchar');
fclose(FID);
or try if CStr2String is faster:
fwrite(FID, CStr2String(C(SortIndex)), 'uchar');
http://www.mathworks.com/matlabcentral/fileexchange/26077

Good luck, Jan
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