Dynamic Matrices in Matlab

Hi!

Yesterday, I had a very similar question, now I want something a bit more advanced. So I have coded already:

data = [234,3,8;457,5,7;611,7,3;234,9,12] 
ID = data(:,1); 
X = data(:,2); 
U = unique(ID) 
data(U(i) == data(:,1),3) 
display data

Now I want to create a matrix, where the first column would be the first column of the data matrix above (i.e. "id"). And all the following collumns would then store the values in the third column of data belonging to this id. So it would look like:

[234, 8,12; 457, 7,0; --- ]

But, obviously, I could not set the dimensions of this matrix from the beginning on, the number of columns would have to be dynamical. Is that possible?

Thanks

[Azzi Abdelmalek]

It's not clear

[MiauMiau]

My question is not clear? So, I would like to have a matrix as follows:

[ 234,8,12; 457,7,0; 611,3,0]

the first column would be the id - and the following columns of the same row would be the third elements in the data matrix belonging to this id. As in the example, it is not clear, how many third column elements each id has - so the number of columns of the matrix would have to be dynamical. Is that possible to programm in matlab?

Answer 1

[Andrei Bobrov]

[a,b,c] = unique(data(:,1));
d = accumarray(c,data(:,3),[],@(x){sort(x)});
n = cellfun(@numel,d);
m = numel(a);
out = [a, zeros(m,max(n))];
for j1 = 1:m
  out(j1,2:n(j1)+1) = d{j1};
end

[Andrei Bobrov]

corrected

[MiauMiau]

the output I get is:

    >> test

data =

     234     3     8
     457     5     7
     611     7     3
     234     9    12

so the data matrix itself...

Answer 2

[Walter Roberson]

Is the number of matching elements possibly different between the id's? If it is, then you cannot do this with a numeric matrix and need to use a cell array instead.