big differences in saving variables

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Abolfazl Nejatian 2020-9-24

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/599020-big-differences-in-saving-variables

评论： Mario Malic 2020-9-26

Hi,

i need to save some tables and variables as Mat and CSV files.

but I have faced a strange behavior on saving the files.

when I save my file and evaluate the time of each of them individually, the saving time much less than I evaluate total saving time.

I also should mention the true elapsed time is a bigger time.

here are my code and output,

folderAddress = 'D:\Nejatian\';
tic
delete([folderAddress 'signals.csv'])
delete([folderAddress 'LatestSignals.csv'])
t1 = toc;
tic
writetable(T,[folderAddress 'signals.csv']);
t2 = toc; 
tic
writetable(lT,[folderAddress 'LatestSignals.csv'])
t3 = toc;
tic
save([folderAddress 'visualData'],'visualData')
t4 = toc;
tic
delete('workspace.mat')
save('workspace.mat');
t5 = toc;
str1 = string(['Deleting CSV files    = ' num2str(t1) 'Sec']);
str2 = string(['Writing  CSV file one = ' num2str(t2) 'Sec']);
str3 = string(['Writing  CSV file one = ' num2str(t3) 'Sec']);
str4 = string(['Saving Mat file from a struct variable = ' num2str(t1) 'Sec']);
str5 = string(['Saving all workspace variables         = ' num2str(t1) 'Sec']);
disp([str1;str2;str3;str4;str5]);  

Deleting CSV files = 0.0320444Sec
Writing CSV file one = 1.99078Sec
Writing CSV file one = 0.273289Sec
Saving Mat file from a struct variable = 0.0120444Sec
Saving all workspace variables = 0.00220444Sec

and the total time is

tic
folderAddress = 'D:\Nejatian\';
delete([folderAddress 'signals.csv'])
delete([folderAddress 'LatestSignals.csv'])
writetable(T,[folderAddress 'signals.csv']);
writetable(lT,[folderAddress 'LatestSignals.csv'])
save([folderAddress 'visualData'],'visualData')
delete('workspace.mat')
save('workspace.mat');
t=toc;
str = string(['Total time  = ' num2str(t) 'Sec']);
disp(str);

Total time = 78.3331Sec

why this big difference happens and how i can speed up my File saving time?

i mean is there any way to parallelize or decompressed the output for reducing the saving file?

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Dana 2020-9-24

编辑：Dana 2020-9-24

Hmm, this doesn't really make sense. The only differences in those two code snippets is the location of some tic/toc statements, which shouldn't meaningfully alter the run time. You're saying you've done this same exercise repeatedly and you keep getting the same result? Are you doing anything in between (e.g., manually altering any files)? Does it matter which order you run these in? Are you sure you've included the tic at the beginning when running the second snippet (if not, it'll compute the elapsed time using the previous call of tic, which could've been on a previous run).

What if you change your initial code to:

tstart = tic;
folderAddress = 'D:\Nejatian\';
tic
delete([folderAddress 'signals.csv'])
delete([folderAddress 'LatestSignals.csv'])
t1 = toc;
tic
writetable(T,[folderAddress 'signals.csv']);
t2 = toc; 
tic
writetable(lT,[folderAddress 'LatestSignals.csv'])
t3 = toc;
tic
save([folderAddress 'visualData'],'visualData')
t4 = toc;
tic
delete('workspace.mat')
save('workspace.mat');
t5 = toc;
t = toc(tstart)
str1 = string(['Deleting CSV files    = ' num2str(t1) 'Sec']);
str2 = string(['Writing  CSV file one = ' num2str(t2) 'Sec']);
str3 = string(['Writing  CSV file one = ' num2str(t3) 'Sec']);
str4 = string(['Saving Mat file from a struct variable = ' num2str(t1) 'Sec']);
str5 = string(['Saving all workspace variables         = ' num2str(t1) 'Sec']);
str = string(['Total time  = ' num2str(t) 'Sec']);
disp([str1;str2;str3;str4;str5;str]);