Matlab – Increasing efficiency of loop that uses datenum function

MATLABoctave

The following loop takes about 700 seconds to run in octave and 22 seconds to run in matlab when the DJI matrix has 21000 rows. How can I increase the efficiency of this?

for i=1:length(DJI)
DJI2(i,1)=datenum(char(DJI(i,2)),'yyyy-mm-dd');
end

Best Answer

Did you remember to preallocate DJI2?

More importantly, you do not need the loop at all. datenum operates on arrays. Try this:

DJI2=datenum(char(DJI(:,2)),'yyyy-mm-dd');

Related Solutions

Running portions of a loop in parallel with Octave

Hmm. I'm more of a MATLAB person than Octave but maybe I can help (if you are still looking for a solution)

This looks like the I'm-reading-in-a-file-but-I-need-to-do-something-different-than-the-tool-provides problem (otherwise you could get away with dlmread which should be pretty fast).

If there were no alternative within Octave to be faster, I'd try using Java (for speed rather than threading); you can call Java from Octave. (though I haven't tried this in Octave, just the MATLAB equivalent)

The calls to str2double look awfully suspicious. You may be able to vectorize that, although a quick speed test on my part seems to confirm that this is a Slow Task, at least from within Octave:

octave-3.0.3.exe:15> s=sprintf('1 2\n3 4');
octave-3.0.3.exe:16> m=str2double(s)
m =

   1   2
   3   4


octave-3.0.3.exe:35> s=randn(5000,5);
octave-3.0.3.exe:36> z=num2str(s);
octave-3.0.3.exe:37> tic; s2=str2double(z); toc
Elapsed time is 18.9837 seconds.

Running code with threads in Octave

According to members on the Octave email list the only way to do this is with the following library. http://atc.ugr.es/javier-bin/mpitb It is designed to be used on multiple machines but looks like it can be used on an individual one as well.

Best Answer

Related Solutions

Running portions of a loop in parallel with Octave

Running code with threads in Octave

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