Preallocation of a vector of structure

Question

Audric Gaspar 2020-11-7

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https://ww2.mathworks.cn/matlabcentral/answers/639830-preallocation-of-a-vector-of-structure

回答： Stephen23 2020-11-20

Hello everyone,

I've been trying to preallocate a vector in which each cell will be a structure of 42 fields like thi:

data = zeros(1,9);
for i=1:9
    if(i~=5)
        data(i) = load(['DPsv0000',num2str(i),'.mat']);
    end
end

Because I need the nine different structures in the same vector for the rest of the code and I want it to be time efficient. However, I can't seem to find a way for the preallocation to work. In fact, doing this, I get the following error:

Conversion to double from struct is not possible.

Error in MECA0062_Gaspar_1 (line 135)

data(i) = load(['DPsv0000',num2str(i),'.mat']);

Can anyone know if it is even possible to do what I'm trying?

Thanks everyone, have a good day!

Audric

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Answer 1

dpb 2020-11-7

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在 MATLAB Online 中打开

You preallocated a double array and then tried to put a struct variable into it. As you discovered, "You can't do that!"

There's not the equivalent per se of preallocating a struct array of empty array elemnts; you just iterate and go on...

d=dir('DPsv0000*.mat']);            % return desired .mat files directory listing
for i=numel(d)
  if contains(d(i).name,'5'), continue, end
  data(i)=load(d(i).name);
end

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Answer 2

Peter Perkins 2020-11-20

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Audric, it seems like dpb understand what you are doing better than I do, but "in which each cell will be a structure of 42 fields" sounds like maybe you are overcomplicating, and that you want an Nx42 table.

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Answer 3

Stephen23 2020-11-20

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在 MATLAB Online 中打开

n = 9;
P = 'absolute or relative path to where the files are saved';
C = cell(1,n);
V = setdiff(1:n,5);
for k = V
    F = sprintf('DPsv%05d.mat',k);
    C{k} = load(fullfile(P,F));
end
S = [C{:}]