- unique already returns a sorted output, so calling sort will waste time.
- duplicating data into lessnum and greaternum likely wastes memory.
- duplicating exactly the same equivalence operations (e.g. indexing inside the loop).
Match each element of one array with each element of other array without loops
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Hello,
I want to match each element of one array with elements of the other array say "cc". Then multiply with a number from the third array. I am doing using loops. The length of arrays are very large therefore it takes couple of hours. Is it possible to do wihtout loops or make it faster. Here is the code, I am doing,
uniquec=sort(unique(cc));
maxc=max(uniquec);
c35p=0.35*maxc;
g=2;
lessnum=uniquec(uniquec<=c35p);
greaternum=uniquec(uniquec>c35p);
gl=linspace(1,2,length(lessnum));
gr=linspace(2,1,length(greaternum));
newC=zeros(size(cc));
for i=1:length(gl)
newC(cc==lessnum(i))= cc(cc==lessnum(i)).*gl(i);
end
for i=1:length(gr)
newC(cc==greaternum(i))= cc(cc==greaternum(i)).*gr(i);
end
2 Comments
Stephen23
on 22 May 2019
Edited: Stephen23
on 22 May 2019
Have you used the profiler to actually check which part of your code is the bottleneck ?
If CC is very large then your code has a few "features" that might prevent it from running efficiently. For example:
It seems that the loops could be replaced with some logical/subscript indexing. As KSSV wrote, you should read about ismember.
Answers (2)
KSSV
on 22 May 2019
Edited: KSSV
on 22 May 2019
Read about ismember, ismembertol and knnsearch.
9 Comments
Stephen23
on 22 May 2019
Edited: Stephen23
on 22 May 2019
" Locb gives number of matches of each number but it do not give indices for them. "
That is incorrect. ismember does not provide any histogram/counting functionality. Its second output are the indices of the values of A in array B. Since R2013a the default is to return the index of the first instance. In your example the first instance of the value 4 is a position 2, the first instance of value 2 is at position 1.
>> Locb(Lia)
ans =
2 1
>> B(Locb(Lia))
ans =
4 2
Image Analyst
on 25 May 2019
You say "Every entery of the loop has to comapre the full array cc."
You might want to take a look at pdist2(), if you have the stats toolbox.
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