writematrix as the recommended alternative to dlmwrite from R2019a

Hello,

I recently moved to Excel 2016 and Matlab R2019a and saw a significant increase in the size of the csv written by dlmwrite.

I also saw that dlmwrite was not recomended starting from R2019a and the suggested alternative was writematrix.

writematrix does not offer all the flexibility of dlmwrite, such as row and columns offsets as well as precision.

Is there any workarounds to still be able to use row and columns offsets with writematrix ?

[Guillaume]

As far as I know, dlmwrite has not changed in the way it works. Can you provide an example that shows this file size increase for csv files written with dlmwrite.

Note that excel is irrelevant for this, neither dlmwrite or writematrix use excel for csv files.

[dpb]

A precision argument of 100 for dlmwrite is ludicrous..."don't do tha!"

Your observation on offset arguments is correct -- TMW did not implement the r, c arguments for text files with writematrix. Sometimes new is not necessarily always improved. If it is needed to use that option with dlmwrite then you'll have to stick with it. That isn't all bad imo, saves fixing previous code that ain't broke for one.

[Guillaume]

Medhi's comment mistakenly posted as an answer moved here:

The observed change in file size was with 2 different PCs (one on windows 10 with excel 2016 and the other one on windows 7 with excel 2010) so i can't readily reproduce the file size increase.

After another look i see that the size increase is coming from the very high precision demanded with dlmwrite (100)

But my issue is not that much about the size but more about the possibility to do offsets with the new preferred writematrix.

As for the size comparison on windows 10:

data = randn(2000,240);

writematrix(data, 'C:\tmp\writematrix.csv'); % Approx. 8MB

dlmwrite('C:\tmp\dlmwrite.csv', data, 'precision',100); % Approx. 25MB

[Mehdi Hacini]

Thanks both for your answers.

Somehow windows 7 with excel 2010 was managing the precision 100 and removing anything unecessary which is not the case anymore leading to the increase in size. After reducing the precision to 16 everything is back to normal and i will stick with dlmwrite for the row and col offsets.

[dpb]

I think Win7 vis a vis 10 had nothing to do with the symptoms and certainly as Guillaume notes Excel has nothing to do with dlmwrite and vice versa. I think the '100' as the precision argument had to be an accidental introduction that wasn't present in the compared-to cases when those files were created.

Answer 1

[Guillaume]

The documentation of writematrix does say that it writes numbers using the longG fomat. longG format is 15 digits of precision (for double), which is about as much precision you can get from double numbers. Using more precision than that is pointless, and going to 100 is completely absurb as dpb said.

So. there's no point trying to be more precise than what writematrix does. If you want to be less precise, there's indeed no way to do that, so you'll have to use dlmwrite.

Similarly,if you want to write into an existing file, you'll also have to use dlmwrite.

For the typical use case, writematrix is a direct replacement. It doesn't mean you have to replace it.

Once again, for csv files, excel is completely irrelevant.