Dynamic Matrices in Matlab

Question

MiauMiau 2012-12-13

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/56513-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

2 个评论
显示无隐藏无

Azzi Abdelmalek 2012-12-13

It's not clear

MiauMiau 2012-12-13

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?

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Andrei Bobrov 2012-12-13

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/56513-dynamic-matrices-in-matlab#answer_68420

编辑：Andrei Bobrov 2012-12-13

在 MATLAB Online 中打开

[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

2 个评论
显示无隐藏无

Andrei Bobrov 2012-12-13

corrected

MiauMiau 2012-12-13

在 MATLAB Online 中打开

the output I get is:

    >> test
data =
     234     3     8
     457     5     7
     611     7     3
     234     9    12

so the data matrix itself...

请先登录，再进行评论。

Answer 2

Walter Roberson 2012-12-13

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/56513-dynamic-matrices-in-matlab#answer_68483

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.