How to save numerical array as file (any format) with different precisions (format) for different columns in the same array?

Hi I am matlab 2016b user. I have one numerical array (950*2 double). When I save this, I want to save 1st column with integer format (no decimal point...I mean %.0f) and to save 2nd column with scientific notation with 16 sigifinicant digits....such as '4.123456789012345e-11'. This is important issue with processing speed in my code. So far, when I use .mat format (binary) with save' function, it gave 9 kb in file size. However, I may need to use no-binary format like...txt....csv...etc. When I tried fprintf and dlmwrite functions with diverse options, 26 kb was record with txt/csv format. I also saw some similar answers using loop for fprintf function, but regarding code running time issue, I hope I can hear another answer using for loop.

Do you know how to do it?

[Guillaume]

I'm not clear on what you're asking. Are you looking for speed or file size? text or binary format?

Binary is always going to be faster and smaller than text.

Why does the format of the columns matter? What is going to read that file?

[Deo]

I need to improve file reading and writing speed by reducing file size. However, for communication and file exchange/share with other person who does not use Matlab, I may need to use txt/csv file. For example, if I just use '-ascii' option, it give 8 digits precision and these are useless for first column and not enough for 2nd column.

Because my two codes generating and reading 6000000 files, so even reducing 1 kb is important for me as total calculation time.

Sorry for my english.

[Walter Roberson]

Consider sending the files in binary, but also providing the person with a program that allows them to view the binary as text. With 6 million files, you can be sure that the other person is not going to read the text of more than a very small fraction of them.

Answer 1

[Guillaume]

One simple way to write that matrix as text according to your specifications:

x = rand(950, 2) .* [100, 1];  %demo data, requires R2016b or later

fid = fopen('somename.csv', 'wt');
fprintf(fid, '%0.f, %.16e\n', x.');
fclose(fid);

[Deo]

Thanks I got this way to switch column and row from other q/a, and this way was what I got 26 kb for each file. I may need to find way to reduce some...useless file information, etc. Thanks for your help :D

Answer 2

[Walter Roberson]

fid = fopen('YourOutputFile.csv', 'wt');
fmt = '%d, %.21e\n';
data = [round(YourArray(:,1)), YourArray(:,2)];
fprintf(fid, fmt, data .');            %transpose is important here
fclose(fid)

The text output will definitely be larger than binary.

[Deo]

Thanks for your help. It is good idea. :D