any suggestions to make this code faster

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huda nawaf
huda nawaf 2012-1-10
hi,
any suggestions to make this code faster, where if take just noofusers 50, it take three or more to complete:
%%%%%%%%%%%%%%%%%%%%%
targetdir = 'd:\matlab11\r2011a\bin\training_set';
nofusers=480189;
targetfiles = '*.txt';
fileinfo = dir(fullfile(targetdir, targetfiles));
f5=fopen('matlab11\r2011a\bin\netflix\un1-17.txt');
z5=fscanf(f5,'%d');
fclose(f5);
for j=1:nofusers
k=1;
for i = 1:17770
thisfilename = fullfile(targetdir, fileinfo(i).name);
f = fopen(thisfilename,'r');
c = textscan(f, '%f %f %s', 'Delimiter', ',', 'headerLines', 1);
fclose(f);
c1 = c{1}; a=find(c1==z5(j));
if ~isempty(a)
c3=c{3};
format long
dat=round(datenum(c3,'yyyy-mm-dd'));
array(j,k)=i;
array(j,k+1)=dat(a);
k=k+2;
else
continue;
end; end; end;
thanks for any advice

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回答（1 个）

Daniel Shub
Daniel Shub 2012-1-10
You should preallocate array to the correct size before the loop. It looks like you could also use a parfor for the first loop. You don't need "format long" in the inner loop (or at all). There are much faster things than datenum (have a search on this site).
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Daniel Shub
Daniel Shub 2012-1-11
In the past, preallocation can considerably speed up code. r2011a is supposed to be better without preallocation, but I haven't tested it and have seen rumors that it is not. I think preallocating the rows will help. Currently, you increase the number of columns by 1, whenever you exceed the current number of columns. You can block allocate and increase it by 10, 100, 1000 ... This will also help speed things up
huda nawaf
huda nawaf 2012-1-14
hi,
please , I did not understand what u mean y this:
Currently, you increase the number of columns by 1, whenever you exceed the current number of columns. You can block allocate and increase it by 10, 100, 1000 ... This will also help speed things up
I hope to give me more details
thanks

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