# "Access Elements of a Nonscalar Structure Array" issue

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Thomas Fournier 2021 年 6 月 7 日
コメント済み: Jan 2021 年 6 月 7 日
Hello,
I try to access data stored in a structure of this type:
I would love to have access easily for exemple to all the masses of all the subsystems, but i cannot manage to do it , i tried : (I pasted the full code at the end)
systems(:).subsystem.mass
but it returned: Reference to non-existent field 'subsystem'.
The real problem has a lot more system than that, do you have an idea on how i could access to all the masses contained in all the subsystems?
Thank you for your help!
I tried to follow this MatLab tutorial but it doesn't seem to work in my case:
clear all
clc
%% creation of the structure
systems=struct();
system1.mass=1000;
system1.CG=[0,1,2];
system1.subsystem.mass=[0;10;100];
system1.subsystem.CG=[0,1,2;3,4,5;6,7,8];
systems.system1=system1;
system2.CG=[0,1,2];
system2.mass=1000;
system2.subsystem.mass=[0;10;100];
system2.subsystem.CG=[0,1,2;3,4,5;6,7,8];
systems.system2=system2;
systems.mass=5000;
systems.CG=[10,20,30];
clear system1
clear system2
systems(:).subsystem.mass
##### 2 件のコメントなしを表示なしを非表示
Stephen23 2021 年 6 月 7 日

Why do you need to brutally CLEAR ALL cached functions from memory?
Is there a reason you cannot just use much more gentle CLEARVARS?
You did not create any non-scalar structures, so the documentation you linked to is not relevant:
isscalar(systems)
ans = logical
1
isscalar(systems.system1)
ans = logical
1
isscalar(systems.system2)
ans = logical
1
Possibly you are confusing the size of a structure with how many fields a structure has (whereas in fact these are totally independent from each other). The design of your scalar structures with multiuple fields does not offer any obvious trivial way to access the nested structures.
Thomas Fournier 2021 年 6 月 7 日
Indeed CLEARALL is not necessary, i recreated the problem in a separated file so it works just well this way.

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### 採用された回答

Jan 2021 年 6 月 7 日
You cannot access fields of deeply nested structs in Matlab. You need a loop to do this.
##### 2 件のコメントなしを表示なしを非表示
Thomas Fournier 2021 年 6 月 7 日
Thank you for your answers, I may have to reconsider how i build my structure then,
But if needed here is a solution which is not pretty but is working:
mass=[];
fn=fieldnames(systems);
for k=1:numel(fn)
if isstruct(systems.(fn{k}))
fn2=fieldnames(systems.(fn{k}));
for l=1:numel(fn2)
if string(fn2(l))=='subsystem'
mass_temp=systems.(fn{k}).subsystem.mass;
mass=[mass,mass_temp];
end
end
end
end
Jan 2021 年 6 月 7 日
Hiding an index in the fieldname as in "system1" is a bad idea. Deeply nested structs are inefficient also, if you need to access nested fields. So restructuring the data might be the best approach.

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### その他の回答 (1 件)

Stephen23 2021 年 6 月 7 日

sys = fakedata()
sys = struct with fields:
system1: [1×1 struct] system2: [1×1 struct] mass: 5000 CG: [10 20 30]
fnm = regexp(fieldnames(sys),'^system\d+\$','match');
fnm = [fnm{:}]
fnm = 1×2 cell array
{'system1'} {'system2'}
fun = @(f)sys.(f).subsystem.mass;
out = cellfun(fun,fnm,'uni',0)
out = 1×2 cell array
{3×1 double} {3×1 double}
Checking (tip for the future: using different values for fake data is a simple sanity check):
out{1}
ans = 3×1
0 10 100
out{2}
ans = 3×1
0 10 100

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