build a matrix from cell

2013 5 8
2 个回答
3 次查看（30 天）

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Dear
I have a cell array which I need to select only first column of each cell separately and put it into a matrix. But each column has different number of row.
can somebody help me ? I think I can build a matrix of zero with the size of my cell and then I put each column separately. However, following effort does not work.
[n,m]=size(X)
A = zeros(100,n);
for i=1:n
A (:,n) = X{n}(:,1)
end

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回答（2 个）

Azzi Abdelmalek
Azzi Abdelmalek 2013-5-8

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X={magic(4),eye(4),rand(4)} % Example
y=cell2mat(cellfun(@(x) x(:,1),X,'un',0))

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Niki
Niki 2013-5-8
编辑：Niki 2013-5-8
Thanks but That is not working for when we have your example X but transposed
X={magic(4),eye(4),rand(4)} % example
X=X';
Now I want to get the first column of each cell into a matrix
Azzi Abdelmalek
Azzi Abdelmalek 2013-5-8
y=cell2mat(cellfun(@(x) x(:,1)',X,'un',0))'
Niki
Niki 2013-5-8
编辑：Niki 2013-5-8
Again thanks but as I explained from very beginning the row of each column is not equal, by running that one I get this error
??? Error using ==> cat
CAT arguments dimensions are not consistent.
Error in ==> cell2mat at 85
m{n} = cat(1,c{:,n});

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Azzi Abdelmalek
Azzi Abdelmalek 2013-5-8
编辑：Azzi Abdelmalek 2013-5-8

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X={magic(5);eye(4);rand(6)}
m=numel(X);
n=max(cellfun(@(x) size(x,1),X));
out=zeros(n,m);
for k=1:m
a=X{k}(:,1);
out(1:numel(a),k)=a;
end

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Niki
Niki 2013-5-8
are you sure this works correctly ? seems like this is a loop forever :-( do you have any other idea which works faster? my laptop is working for 10 min and still not finished
Azzi Abdelmalek
Azzi Abdelmalek 2013-5-8
What is the size of X?
Niki
Niki 2013-5-8
[n,m]=size(peaks)
n =
8300
m =
1

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Niki
Niki
2013-5-8

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