Call fields of struct more efficiently in a loop

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Tejas
Tejas 2020-8-22
编辑： Tejas 2020-8-22
I want to do the following more efficiently.
vec.time = [1000,5000];
vec.nest = {'center','corner'};
vec.grid = [50,100,1000];
for i.time = 1:length(vec.time)
p.time = vec.time(i.time);
for i.nest = 1:length(vec.nest)
p.nest = vec.nest(i.nest);
for i.grid = 1:length(vec.grid)
p.grid = vec.grid(i.grid);
%Code
end
end
end
Essentially, the fields of the structs vec, i, p will be the same. The vec struct contains all the values that I want to run in a loop, the i struct acts as a counter for them, and the p struct runs the code with the particular value selected. Is there a way such that I can call the fields by their order number rather than their name? Though, I do want the p struct with all the field names in the end, since the rest of the code depends on it. Thank you!
Edit: I've been looking into similar problems, and I think it might be done using struct2cell and cell2struct. For this particular example, if I have an array as
order = [1 1 1 ; 1 1 2 ; 1 1 3 ; 1 2 1 ; 1 2 2 ; 1 2 3 ;
2 1 1 ; 2 1 2 ; 2 1 3 ; 2 2 1 ; 2 2 2 ; 2 2 3];
then what I can do is
vec_cell = struct2cell(vec);
fields = fieldnames(vec);
p_cell = cell(length(vec_cell),1);
for i_order = 1:length(order)
for i_cell = 1:length(vec_cell)
p_cell{i_cell} = vec_cell{i_cell}(order(i_order,i_cell));
end
p = cell2struct(p_cell,fields);
%Code
end
While this may not be as efficient, it certainly seems more robust, since I only need to add information to the vec struct, and it would calculate the p struct for every iteration. I do need help with constructing the order array, given the number of fields in the vec struct, and the length of each field. Thank you!
Edit2: I realised that values in vec.nest cannot be assigned this way, since they are in a cell, while others are in an array. But I can resolve this by assigning values to them (1 is 'center', 2 is 'corner').
  1 个评论
Walter Roberson
Walter Roberson 2020-8-22
It is not permitted to use a structure field as a for loop control variable. Only simple unindexed variables can be used.

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回答（1 个）

Walter Roberson
Walter Roberson 2020-8-22
Is there a way such that I can call the fields by their order number rather than their name?
fn = fieldnames(appropriate_structure);
for K = 1 : length(fn)
appropriate_structure.(fn{K}) %effectively call by number
end
Though, I do want the p struct with all the field names in the end
Consider using structfun()
Note that structfun() is not necessarily more efficient than a for loop: it is more compact than a for loop, but structfun does a for loop internally.

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