index exceed the number of arrays elements

Question

Julio Ferreira 2022-8-10

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1777250-index-exceed-the-number-of-arrays-elements

评论： Julio Ferreira 2022-8-10

采纳的回答： Kevin Holly

在 MATLAB Online 中打开

i have this problem with number of array elements . Index must not exceed 124.

How do i solve this? Thanks

length_collective=length(Collective); %equals to 124
length_single=length(single); %equals to 393
for i=1:1:length(Collective)
    aux=[];
    for j=1:1:length(single)
        if(single(j)>Collective(i) && single(j)<Collective(i+1)  )
            aux=single(j);
        end
        if( (single(j)>Collective(length(Collective)-1 )) && i==length(Collective)-1 )
            aux=single(j);
        end
    end
end

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Answer 1

Kevin Holly 2022-8-10

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https://ww2.mathworks.cn/matlabcentral/answers/1777250-index-exceed-the-number-of-arrays-elements#answer_1024425

在 MATLAB Online 中打开

Collective = rand(1,124);
single = rand(1,393);
length_collective=length(Collective) %equals to 124
length_collective = 124
length_single=length(single) %equals to 393
length_single = 393
for i=1:1:length(Collective)-1 % I added a minus one here
    aux=[];
    for j=1:1:length(single)
        if(single(j)>Collective(i) && single(j)<Collective(i+1)  )% because when i =124, this line tries to read Collective(125), which does not exists (exceeds 124).
            aux=single(j);
        end
        if( (single(j)>Collective(length(Collective)-1 )) && i==length(Collective)-1 )
            aux=single(j);
        end
    end
end

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Julio Ferreira 2022-8-10

thank you, it was easier than i tought

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Answer 2

dpb 2022-8-10

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https://ww2.mathworks.cn/matlabcentral/answers/1777250-index-exceed-the-number-of-arrays-elements#answer_1024430

在 MATLAB Online 中打开

length_collective=length(Collective); %equals to 124
length_single=length(single); %equals to 393
for i=1:1:length(Collective)
  ...

Why compute and save variables of the length and then not use them but call the function again?

NB: As side note, length() is a risky function being as it is defined as max(size()) so that one can get either the number of rows or number columns for a 2D array, depending on its size. It's OK for known 1D vectors; otherwise, use size() with the specific dimension of interest; rarely is the orientation not of importance where length is actually the desired result.

    ...
    aux=[];
    for j=1:1:length(single)
        if(single(j)>Collective(i) && single(j)<Collective(i+1)  )
            ...

You're running the loop over the total number of elements in the array but then addressing the next element past the one of the loop index -- henc, when you reach the last element, the next one is outside array bounds.

The expedient fix in the loop is to iterate only up to length_single - 1