how to initialize a vector of structure

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XAXRXTX
XAXRXTX 2014-3-4
评论： Jos (10584) 2014-3-4
hello
so i have the example abouve
for i = 1 : n
structure.a = .......
structure.b = .......
.
.
structure.z = .......
my_vector(i) = structure;
end
the question is how i can preallocte the space size for the vector my_vector ?
thanks in advance
  1 个评论
James Tursa
James Tursa 2014-3-4
What is the stuff on the right-hand-side? Are you attempting to just get my_vector pre-allocated to hold the correct fields but not actually have anything in the field elements?

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回答（4 个）

Mischa Kim
Mischa Kim 2014-3-4
XAXRXTX, check out the documentation.
  1 个评论
XAXRXTX
XAXRXTX 2014-3-4
thanks Mischa Kim
but, but I do not want to initialize every field of the structure !!!

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Kan-Hua
Kan-Hua 2014-3-4
To preallocate memory, you need to put some values into the data structure that you are using. I think it's the design of Matlab. For example, to preallocate a memory for a 25x25 matrix, you need
mtx=zeros(25)
or
mtx=ones(25)
It is the same case for a structure array. To preallocate the memory space, you have to put some dummy values into every fields of the structure.
Jos (10584)
Jos (10584) 2014-3-4
编辑：Jos (10584) 2014-3-4
As Mischa pointed out: preallocation of structures is easy:
S(1:5) = struct('a',zeros(10,1),'b','empty')
  2 个评论
XAXRXTX
XAXRXTX 2014-3-4
but , it's tedious to write S = struct('a','empty', 'b','empty', 'c','empty' ,'d','empty'...
................, 'z','empty');
there 's no other solution in fonction of the number of the structure field ???
Jos (10584)
Jos (10584) 2014-3-4
If your fieldnames are known and you all want to set them to the same default value, in a 1-by-N array of structures S , try this
fn = {'a','b','c','d'} ; % this can be coded as well ...
value = zeros(1,10) ;
N=5 ;
S(1:N) = cell2struct(repmat({value},numel(fn),1),fn,1)

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Kan-Hua
Kan-Hua 2014-3-4
You can consider using table instead of structure array to store your data, which gives some flexibility to access the members. However, the version of you Matlab has to be 2013b or later.
Here's some example code of using table, which may solve your problem:
% initialise a table
zarray=zeros(1,3);
T=array2table(zarray,'VariableNames',{'colA','colB','colC'});
%show the initial values of the array
disp(T);
% assign the first row of the table by using names
T.colA(1)=1;
T.colB(1)=2;
T.colC(1)=3;
%Print out the table
disp(T);
% Alternatively, you can do it by index
for i=1:size(T,2)
T(2,i)={i*2};
end
% Print out the table
disp(T)

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