Adding elements to the ends of vectors inside a cell array of vectors
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Mark Szlazak
le 29 Juil 2021
Commenté : Mark Szlazak
le 2 Août 2021
Is there a way to add elements to the ends of vectors that are inside a cell array of vectors which would be faster than the following code that uses a for-loop?
x = rand(1,20);
i1 = [1,7,11];
i2 = [6,10,20];
xLower = [0.1 0.2 0.3];
xUpper = [100 200 300];
tic();
for r = 1:length(i1)
xRegion{r} = [xLower(r) x(i1(r):i2(r)) xUpper(r)];
end
toc();
xRegion
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Eike Blechschmidt
le 29 Juil 2021
You could use arrayfun:
arrayfun(@(l,i1,i2,u) [l x(i1:i2) u], xLower,i1,i2, xUpper, “uniform“, false)
This is untested but should be faster.
8 commentaires
Eike Blechschmidt
le 1 Août 2021
Modifié(e) : Eike Blechschmidt
le 1 Août 2021
You have to differentiate between allocating the cell array and allocating for the actual content of the cell array. Basically your cell array is just storing a bunch of pointers to the actual arrays of double you create in your for loop.
So it would only make sense to do the following which in your current example does not bring any benefit as i1 is quite small (I tried that on my machine):
xRegion = cell(size(i1))
I don't know a way to pre allocate memory for the created double arrays from your loop which would not involve a loop.
Depending on how you later processes the data it could could be worth trying just to use a pre-allocated doble array instead and set all not needed fields to nan. Again just gussing if that even does speed up your code.
arrSize = i2 - i1 + 3;
xRegion1 = nan(length(i1), max(i2 - i1 + 2));
for r = 1:length(i1)
xRegion1(r, 1:arrSize(r)) = [xLower(r) x(i1(r):i2(r)) xUpper(r)];
end
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