For loop get an error of "size of the right side is 0-by-1"

Question

Nao 2022-11-12

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评论： Nao 2022-11-12

Hi.

I have 2 sets of vectors B and C, both 79x1, and want to extract the max point (peak) between the corresponding rows of B and C. Here is the code I have so far:

peak = B
for i = 1:length(B)
    peak(i,1) = max(A(B(i,1):C(1,1)));
end

But this gets an error of "Unable to perform assignment because the size of the left side is 1-by-1 and the size of the right side is 0-by-1".

I have another data set and the above code worked perfectly fine for it. Moreover, when it's taken out of the for loop and I specify a number for "i" for example:

peak(1,1) = max(A(B(1,1):C(1,1)))

This runs without a problem.

Can someone please help me identify the issue? Thank you in advance!

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Answer 1

KSSV 2022-11-12

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peak = B
for i = 1:length(B)
    c = A(B(i,1):C(1,1)) ; 
    if ~isempty(c)
        peak(i,1) = max(c);
    end
end

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KSSV 2022-11-12

Sometimes the right side is empty. So you cannot assign a empty matrix as an element to in an initialised array. Anyways what you are trying is not a good coding practise.

Nao 2022-11-12