How to convert a layered structure into arrays.

Question

John Petersen 2021-3-18

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/777157-how-to-convert-a-layered-structure-into-arrays

编辑： Matt J 2021-3-18

I have a structure like this

A.a.b.first, A.a.b.second, A.a.b.third
A.c.d.first, A.c.d.second, A.c.d.third
A.e.f.first, A.e.f.second, A.e.f.third

I want to extract the fields "first", "second" and "third" into arrays so that one array has all the firsts, another has all the seconds, and a thrid and all the thirds. Is there a simulink method to use or a matlab function? I am currently brute forcing it in matlab code. That is,

B(1) = A.a.b.first
B(2) = A.c.d.first
B(3) = A.e.f.first

and so forth. So it would be much better to have a loop or something even more streamlined.

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Matt J 2021-3-18

编辑：Matt J 2021-3-18

Are the desired fields always at a fixed depth (4 fields deep in your example)? Also, if the field names are not a simple alphabetical progression, what decides the order of the elements in B(i)? We need to know the general pattern before a solution can be recommended.

John Petersen 2021-3-18

编辑：John Petersen 2021-3-18

No. Most are four, but some are only three deep. There is a bus in simulink that defines the order. Is it possible to use that? There is also an enum that is used in the code that defines the same order.

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Answer 1

Matt J 2021-3-18

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https://ww2.mathworks.cn/matlabcentral/answers/777157-how-to-convert-a-layered-structure-into-arrays#answer_651972

编辑：Matt J 2021-3-18

在 MATLAB Online 中打开

Here's a way you can recursively search down through a tree of nested structs. Since I don't know how you want to handle multiple occurrences of the target field name (e.g. "first") on the same branch of the treee, I propose one possibility:

A.b.c.d.e.first=3;
A.g.h.first=4;
out = findField(A,'first')
out = 1×2 cell array
    {[3]}    {[4]}
function out=findField(S,tfield)
  if ~isstruct(S)
     
     out=[];
  elseif isfield(S, tfield)
      out=S.(tfield); %found a match
      
  else%recurse 
      
    f=fieldnames(S);
      
    if numel(f)==1  
      
        out=findField(  S.(f{1})  , tfield);
        
    else   
      for i=1:numel(f)
       out{i}=findField(  S.(f{i})  , tfield);
      end
    end
    
  end
end

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John Petersen 2021-3-18

Thanks, that looks like it might work.

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Answer 2

Matt J 2021-3-18

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https://ww2.mathworks.cn/matlabcentral/answers/777157-how-to-convert-a-layered-structure-into-arrays#answer_651927

编辑：Matt J 2021-3-18

在 MATLAB Online 中打开

A more automated option,

f=string(num2cell('a':'z'));
for i=1:13
    B(i)=A.(  f(2*i-1)  ).(  f(2*i)  ).first;
    C(i)=A.(  f(2*i-1)  ).(  f(2*i)  ).second;
    D(i)=A.(  f(2*i-1)  ).(  f(2*i)  ).third;
    
end