Alternative to using Multi-level field struct
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Science Machine
on 7 Jul 2022
Edited: Bruno Luong
on 8 Jul 2022
I am taking two populated structs and re-ordering them, so that I can do an operation(such as fft), on the end-most field's elements, eg
bigNum=1e4;
for b=1:bigNum
for a=1:bigNum
val=Struct_A(a).dat(b);
Struct_B(b).dat(a)=val;
val2 = fft(Struct_B(b).dat(:);
end
end
I do this also with 3-layered field structures such as Struct_C(f).fielde(e).fieldd(d).dat.
- Is there a more efficient way to handle this reordering?
- Can I vectorize this or otherwise speed this up? I am using parfor loops, but, it seems just the idea of re-ordering structures is a bad paradigm when considering large data
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Accepted Answer
Michael Van de Graaff
on 7 Jul 2022
I gave it shot.
n = 1000;
s(n) = struct();
for ii = 1:n
for jj = 1:n
s(ii).a(jj) = ii;%this is just building the original struct
end
end
tic
for ii = 1:n
for jj = 1:n
val = s(ii).a(jj);
s2(jj).a(ii) = val;% do the loop like you have
end
end
toc
%now lets try something without loops, should be faster for large n
tic
tmp = cell2mat(squeeze(struct2cell(s))).';
tmp2=mat2cell(tmp,ones(1,n),[n]);
s3 = cell2struct(tmp2,fieldnames(s),4);
toc
% and let's do a loop to ensure s2 and s3 are the same
s_diff = zeros(n);
for ii = 1:n
for jj = 1:n
s_diff(ii,jj) = s2(ii).a(jj)-s3(ii).a(jj);
end
end
if max(abs(s_diff(:)))==0
disp('success') %I got success
else
disp('failure')
end
3 Comments
Michael Van de Graaff
on 8 Jul 2022
"would be possible to eschew structures altogether?"
Are you familiar with cell arrays? That seems like precisely what you are looking for, as they can be n-dimsionsal and each cell can contain whatever data type, including arrays of differeing sizes. You don't get the built in clarity of the fieldnames, but a GPU don't need no fieldnames :D (I have literally no knowledge of how GPU implementations work fyi)
More Answers (1)
Bruno Luong
on 8 Jul 2022
Edited: Bruno Luong
on 8 Jul 2022
It seems you just burry an array into nested structures for no apparent reason other than using struct with a fieldname for a sake of it speaks to you.
Undo that and think like a computer:
% Generate dummy data
a = 10; % your big number
b = 11; % another of your your big number
for i=1:a
for j=1:b
STRUCTA.A(i).B(j) = rand();
end
end
% Undo the thing to getback numerical array
a = length(STRUCTA.A);
b = length(STRUCTA.A(1).B);
AB=reshape([STRUCTA.A.B],[b,a]); % deepest nested length first, ...
% Simply work on the array, that how MATLAB should be used
% If you want to swap a/b dimension, transpose AB, no need for
% the ugly double for-loop as you do.
val2 = fft(AB,[],2)
2 Comments
Bruno Luong
on 8 Jul 2022
Edited: Bruno Luong
on 8 Jul 2022
With three (four) levels you have to do 2-step
...
AB = [STRUCTA.A.B];
ABC = reshape([AB.C],[c b a]);
...
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