fread() optimization binary file
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I am reading a 40 MB file with three different ways. But the first one is way faster than the 2 others. Do you guys have an idea why ? I would rather implement condition in loops or whiles to separate data than load everything with the first quick method and separate them then - memory saving -
LL=10000000;
fseek(fid,startbytes, 'bof');
%%Read all at once %%%%%%%%%%%%%%%%%%%%%%
tic
AA(:,1)=int32(fread(fid,LL,'int32'));
toc
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
fseek(fid,startbytes,'bof');
%%Read all using WHILE loop %%%%%%%%%%%%%
tic
i=0;
AA2=int32(zeros(LL,1));
while i<LL
i=i+1;
AA2(i,1)=fread(fid,1,'int32');
end
toc
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
fseek(fid,startbytes,'bof');
%%Read all using FOR loop %%%%%%%%%%%%%%%
tic
AA3=int32(zeros(LL,1));
for i=1:LL
AA3(i,1)=fread(fid,1,'int32');
end
toc
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
Elapsed time is 0.312916 seconds.
Elapsed time is 138.811520 seconds.
Elapsed time is 116.799286 seconds.
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Answers (1)
Walter Roberson
on 26 Jan 2013
Consider reading data in chunks (e.g., 4 Kb): that should give you better speed than reading single int32 at a time, but would also reduce the amount of memory needed.
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