for 1:x with unkonw x

Hi everybody,

i have an array like this:

ARRAY

X Y Z C

-3 4 5 1

5 6 2 2

4 4 9 1

6 6 7 2

4 6 2 3

9 9 7 3

where C goes from 1 to x (x unknow). I want to create a for to have x arrays with XYZ associated with C, like this:

for k=1:x

A(1:k)=[ARRAY(:,1),ARRAY(:,2),ARRAY(:,3),ARRAY(:,4)==1:k]

end

A1

X Y Z

-3 4 5

4 4 9

A2

X Y Z

5 6 2

6 6 7

A3

X Y Z

4 6 2

9 9 7

Thank you!

Answer 1

[madhan ravi]

Don't think of naming variables dynamically (https://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval ) use cell instead:

a=[-3  4  5  1
5  6  2   2
4  4  9   1
6  6  7   2
4  6  2   3
9  9  7   3];
u=unique(a(:,4));
A=cell(1,numel(u));
for i = 1:numel(u)
      idx = (a(:,4) == u(i)); % edited after Jan's comment
%     idx=ismember(a(:,4),u(i));
    A{i}=a(idx,1:3);
end
celldisp(A)

Gives:

A{1} =
 
    -3     4     5
     4     4     9
 
A{2} =
 
     5     6     2
     6     6     7
 
A{3} =
 
     4     6     2
     9     9     7

[Jan]

+1. You can replace idx=ismember(a(:,4),u(i)) by the simpler and faster

idx = (a(:,4) == u(i));

[madhan ravi]

Vielen Dank Jan !

[Riccardo Rossi]

Thank you very much, it's run!

Just another question. I need to calculate the X Y Z's mean of A{1},A{2},...,A{x}, how can i do it?

Thank you a lot!

[madhan ravi]

Anytime :)

mean_of_X_Y_Z_in_each_cell=cellfun(@mean,A,'un',0)

[Riccardo Rossi]

So grateful!

Answer 2

[KSSV]

A = [-3  4  5  1
5  6  2   2
4  4  9   1
6  6  7   2
4  6  2   3
9  9  7   3 ] ;

C = A(:,end) ;
[c,ia,ib] = unique(C) ;
N = length(c) ;
iwant = cell(N,1) ;
for i = 1:N
    iwant{i} = A(C==c(i),1:3) ;
end