access elements of vector within struct

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dleal
dleal on 22 Apr 2022
Edited: Matt J on 22 Apr 2022
Hi all,
I want to update the values of a vector, within a struct, recursively, in a for loop. In particular, I am receiving real time inputs(yobs, observations in milliseconds for several hours), for different objects, which I am storing within a struct (S, for example) :
yobs = randn(1,100); %vector of observations, which i am receiving one by one
S = struct;
S.A = nan(1,100); %preallocate for speed
for ii = 1:numel(yobs)
temp = S.A;
temp(ii) = yobs(ii);
S.A = temp;
end
Accessing the struct in this way, requires a copy of S.A into temp, which will be slow since the iterations will be over millions of observations.
Alternatively, I could not preallocate S.A, but that will also consume time. Is it absolutely necessary to copy the previous values of S.A into a temporary variable as above? thank you

Accepted Answer

Voss
Voss on 22 Apr 2022
"Is it absolutely necessary to copy the previous values of S.A into a temporary variable as above?"
No, it's not necessary.
yobs = randn(1,100); %vector of observations, which i am receiving one by one
S = struct;
S.A = nan(1,100); %preallocate for speed
for ii = 1:numel(yobs)
S.A(ii) = yobs(ii);
end
  1 Comment
dleal
dleal on 22 Apr 2022
thank you _ ... for some reason I thought S.A(ii) would produce a struct array. I keep confusing S(ii).A and S.A(ii)... thank you!

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More Answers (1)

Matt J
Matt J on 22 Apr 2022
Edited: Matt J on 22 Apr 2022
S.A doesn't appear to be playing any role within your loop at all. You could just as easily have done,
temp = nan(1,100); %preallocate for speed
for ii = 1:numel(yobs)
temp(ii) = yobs(ii);
end
S.A = temp;

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