Calculate values of struct of struct

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Julian
Julian 2023-9-4
评论： Julian 2023-9-5
I have a struct with several fieldnames, each of them is again a struct and has a fieldname "P". This "P" is an array.
I want to calculate the sum of all "P "s like:
s.s1.P = (1:20).'; % For simplicity I have assigned dummy values to the "P "s.
s.s2.P = (1:20).';
s.s3.P = (1:20).';
% ...
result = s.s1.P + s.s2.P + s.s3.P % + ...
I have already a solution with a for loop:
field = fieldnames(s);
result = zeros(size(s.(field{1}).P));
for i = 1:length(field)
result = result +s.(field{i}).P;
end
I also tried to use "structfun" but were not able to get this result.
Is it possible to calculate this problem with "structfun" or another function or is the for loop the final solution for this problem?
  1 个评论
Stephen23
Stephen23 2023-9-4
Rather than forcing pseudo-indices into fieldnames you should simply use a structure array, as dpb showed.

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采纳的回答

Bruno Luong
Bruno Luong 2023-9-4
编辑：Bruno Luong 2023-9-4
Ran in:
Single line (work for fields with struct NOT objects of class, struct is NOT some sort of class)
s.s1.P = (1:20).'; % For simplicity I have assigned dummy values to the "P "s.
s.s2.P = (1:20).';
s.s3.P = (1:20).';
sum([cat(1,struct('sx',struct2cell(s)).sx).P],2)
ans = 20×1
3 6 9 12 15 18 21 24 27 30

更多回答（2 个）

dpb
dpb 2023-9-4
编辑：dpb 2023-9-4
Ran in:
The problem of using sequentially-named fields in the struct instead of an array of struct; there's no good way to process the resulting variables or struct fields programmatically when do so.
structfun applies the function to each field of a scalar struct so it isn't the tool for the purpose here, anyway, you're trying to process across fields, not within each. And, arrayfun is for an array but you didn't use an array to hold the similar data, you chose to use multiple fields instead. A 2D array would have been an alternate choice that could have handled easily...
s.P = (1:20).';
s.P = [s.P (1:20).'];
s.P = [s.P (1:20).'];
result = sum(s.P,2)
result = 20×1
3 6 9 12 15 18 21 24 27 30
Or, alternatively, as a struct array
s.P = (1:20).';
s(2).P = (1:20).';
s(3).P = (1:20).';
result = sum([s.P],2)
result = 20×1
3 6 9 12 15 18 21 24 27 30
  7 个评论
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Bruno Luong
Bruno Luong 2023-9-4
编辑：Bruno Luong 2023-9-4
Ran in:
No
D=delaunayTriangulation(rand(10,2))
D =
delaunayTriangulation with properties: Points: [10×2 double] ConnectivityList: [12×3 double] Constraints: []
structfun(@(D)D.Points, D)
Error using structfun
Inputs to STRUCTFUN must be scalar structures.
Sorry my first remark on structfun on class is not applicable int the present context, since s is still a struct with 3 fields. structun can be applied on s.
Julian
Julian 2023-9-5
Yes structfun was used on s, a struct and it's not posible to use structfun on class objects.

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Bruno Luong
Bruno Luong 2023-9-4
编辑：Bruno Luong 2023-9-4
Ran in:
Honestly I prefer the for-loop
s.s1.P = (1:20).'; % For simplicity I have assigned dummy values to the "P "s.
s.s2.P = (1:20).';
s.s3.P = (1:20).';
c = struct2cell(structfun(@(sf) sf.P, s, 'UniformOutput', false));
sum(cat(2,c{:}),2)
ans = 20×1
3 6 9 12 15 18 21 24 27 30
  2 个评论
dpb
dpb 2023-9-4
Given the already bad idea of having created the sequentially-named fields, agree, the for loop is the way; as your example shows, to do anything else gets far too convoluted and undoubtedly would be slower besides.
At least with struct fields, one can programmatically access them w/o the eval abomination.
Julian
Julian 2023-9-4
Thanks for the solution.
Unfortunately, I already came up with this, but I didn't like this huge nesting of functions either.
I understand why you would prefer the for-loop.

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