access elements of vector within struct

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

Answer 1

[Voss]

"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

[dleal]

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!

Answer 2

[Matt J]

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;