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arraysmatlabmemory
user3536870
user3536870

Reputation: 249

MATLAB preallocating space to unroll different size matrices from cell arrays

I am trying to allocate space to my for loop but it just won't work.

I have looked at all the similar questions and matlab help and it doesn't make any difference. I must be missing something.

xt = [];
yt = [];

for ii = 1:size(result,1)
        x = result{ii,1}(:,1);
          xt = [xt;x];
        y = result{ii,1}(:,2);
          yt = [yt;y];
end

And my attempt at precollacting space for xt has been

xt = zeros(size(result,1),1);

with no results. I think my problem might be that result is a cell array??

Upvotes: 0

Views: 46

Answers (1)

Ander Biguri
Ander Biguri

Reputation: 35525

If you concatenate you don't need to prealocate. If you prealocate don't concatenate!

 xt = [xt;x];

The previous line will take xt, will put x amount of NEW values in the end of it, appended. It will not substitute the values of xt.

To be able to allocate memory for different sizes of a cell array youll need to know the number of elements of each one.

sizes=zeros(size(result,1),1);
for ii=1:size(result,1)
    sizes(ii)=size(result{ii},1);  %//get the size of the matrix
end
%// now we know the sizes

xt=zeros(sum(sizes),1); %the total number is the sum of each of them

%// handle the first special case
xt( 1:sizes(1) )=result{1,1}(:,1);
%// add the rest
for ii = 2:size(result,1)
    xt( 1+sum(sizes(1:ii-1)) : sum(sizes(1:ii)) )= result{ii,1}(:,1);
end

Upvotes: 2

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