MATLAB: Nested Struct Preallocated Memory

preallocate memory nested struct

Good Day,
What is the best way to preallocate for a nested struct? I'm currently looping as follows but looking around it doesn't seem the way to go:
for i = 1:n
 for j = 1:x
 Field.SubField(i).Element(j).X = zeros(3,1)
 Field.SubField(i).Element(j).Y = zeros(3,1)
 Field.SubField(i).Element(j).Z = zeros(3,1)
end
end

Best Answer

With the shown method, the array Field.SubField and Field.SubField(i).Element still grow in each iteration. So a pre-allocate happens for the fields X, Y, Z only. Better:
for i = n:-1:1    % Backwards for implicit pre-allocation!

  for j = x:-1:1  % Backwards for implicit pre-allocation!
    Field.SubField(i).Element(j).X = zeros(3,1)
    Field.SubField(i).Element(j).Y = zeros(3,1)
    Field.SubField(i).Element(j).Z = zeros(3,1)
  end
end
If in the first iteration Field.SubField(n).Element(x) is created, and this creates Field.SubField(1) and Field.SubField(n).Element(1) implicitly also.
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