How do structures work?

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Chiara Modenese
Chiara Modenese 2011-4-13
Hi there. Say that I use an array of structures and that then I want to create an array like:
[ss.phi] % ss is the array of structures, and phi a number
Now, the above works just fine but what does not work is:
[ss.phi(1)] % this time phi is an array of doubles and I only want to keep the first element
Why is the last case wrong? And how to fix it?
Thanks. Chiara

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回答（2 个）

Jarrod Rivituso
Jarrod Rivituso 2011-4-13
I think MATLAB doesn't let you nest subscripts like that. However, there are workarounds. Is this what you are looking for:
>> var(1).a = [3 4];
>> var(2).a = [5 6];
>> var(1).b = 10;
>> var(2).b = 13;
>> getFirstElementFcn = @(x) x(1);
>> allFieldsA = {var.a};
>> cellfun(getFirstElementFcn, allFieldsA)
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Jarrod Rivituso
Jarrod Rivituso 2011-4-13
Note that I've created an anonymous function to go through and grab the first element, and then I've put all the field values in a structure array, and then finally I apply the function to the field values within the cell.

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Oleg Komarov
Oleg Komarov 2011-4-13
ss.phi = rand(10);
ss.phi = ss.phi(1)
Saying it's not working is as far as you can get from a clear description of a problem.
EDIT Following Jarrod's interpretation (which by the way, I now think, is your situation), another way:
var(1).a = [1 2; 3 4];
var(2).a = [5 6; 7 8];
temp = cat(3,var.a);
squeeze(temp(1,1,:))
Or fetching elements in a loop (no vectorized way available):
% Preallocate
...
for s = 1:numel(var)
out(...) = var(s).a(1)
end
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Chiara Modenese
Chiara Modenese 2011-4-13
Well, this is not what I would exactly define as a satisfactory answer. However, I can see there are many workarounds (thanks to Jarrod, too).
Chiara

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