How do I preallocate this loop?

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Ryan
Ryan on 8 Aug 2013
Hello
I'm trying to make my program run faster and it suggests to preallocate this loop. Anyone know how convert this loop?
% code
for i = 1:1:5
z(i) = x(zipfind - 1 + i);
end
Thanks!

Accepted Answer

Evan
Evan on 8 Aug 2013
Edited: Evan on 8 Aug 2013
Here is the loop with preallocation:
z = zeros(5,1) % preallocation
for i = 1:1:5
z(i) = x(zipfind - 1 + i);
end
Also, it looks as if you could possibly remove the looping altogether:
x = randi(20,20,1);
zipfind = randi(20);
zloop = zeros(5,1);
for i = 1:5
zloop(i) = x(zipfind - 1 + i);
end
zvec = x(zipfind - 1 + (1:5));
And compare the results of zloop and zvec:
>>zvec
zvec =
14
4
3
10
20
>> zloop
zloop =
14
4
3
10
20
So, basically, you could just replace that entire loop with:
z = x(zipfind - 1 + (1:5));

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