Preallocating a structure with a changing number of rows within a field

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Christoper Angelo Malayan 2021-1-9

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/712443-preallocating-a-structure-with-a-changing-number-of-rows-within-a-field

评论： Bruno Luong 2021-1-10

采纳的回答： Bruno Luong

G.mat

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Hi all. I'm relatively new in MATLAB and I'm trying to optimize my code.

I have this function:

function G = GroupM1(A,num_K)
%Grouping r according to m1 and arranging from high to low
for i = [1:num_K]
    G(i).dist = A(A.m1 == i,:);
   
    G(i).dist = sortrows(G(i).dist, string(i),'ascend'); 
end 
end

It produces a structure 'G' (see attached file)

'A' is just a 100x17 table. And In this case, num_K == 9. The number of rows in structure 'G' is always equal to num_K.

My questions is:

How can I preallocate this structure 'G' that has 1 field (.dist) containing different sized tables so that the row number is always equal to num_K?

Any help is appreciated. Thank you.

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Answer 1

Bruno Luong 2021-1-9

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https://ww2.mathworks.cn/matlabcentral/answers/712443-preallocating-a-structure-with-a-changing-number-of-rows-within-a-field#answer_594123

There is no need to preallocate a field (or in fact any variable) if you don't grow the array itself in a loop, which is your case.

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Christoper Angelo Malayan 2021-1-10

Hi Bruno. Thanks for answering.

But the table sizes within the fixed structure 'G' is changing and MATLAB advices me to preallocate it i.e. the rows of struct G.dist is always == to num_K but the dimension of the table G(n).dist will change every iteration.

Any tips on how to preallocate these tables within the struct?

Thanks