Matrix value to store as matrix index

Hello All,

I have a matrix A and I would like its values to be stored as its indeces in another matrix

A = [2 2 1 1 1; 3 3 3 0 2; 5 4 5 0 3]

A =

     2     2     1     1     1
     3     3     3     0     2
     5     4     5     0     3
% the result matrix AA should look like:
AA =

     0     0     1     1     1
     2     2     0     0     2
     3     3     3     0     3
     0     4     0     0     0
     5     0     5     0     0

you see how the 2 at A11 shows up on AA21 (because 2 is the second index in the first column) and 5 shows up on the fifth row (AA51). Anyhelp would be appreciated. Thnx

[madhan ravi]

What happens to A11 ?

[Ahsan]

A11 value is two so --> in AA it should be in row two

Answer 1

[Rik]

The code below works. I'll try to find a better way, but in the meantime you can use this.

A = [2 2 1 1 1; 3 3 3 0 2; 5 4 5 0 3];
AA=zeros(max(A(:)),size(A,2));
for r=1:size(A,1)
    for c=1:size(A,2)
        if A(r,c)~=0
            AA(A(r,c),c)=A(r,c);
        end
    end
end
disp(AA)

And this is my try without loops:

A = [2 2 1 1 1; 3 3 3 0 2; 5 4 5 0 3];
sz=[max(A(:)),size(A,2)];
rowval=A;rowval(rowval==0)=NaN;
colval=(1:sz(1)).*ones(size(A,1),1);
%or on older releases (before R2016b):
%colval=bsxfun(@mtimes,1:sz(1),ones(size(A,1),1));
subs=[rowval(:),colval(:)];
subs(isnan(subs(:,1)),:)=[];
AA=accumarray(subs,val,sz,[],0);
disp(AA)

[Ahsan]

Thank you so much. It did the trick

Cheers

Answer 2

[Andrei Bobrov]

ii = (1:5)';
AA = any(ii == permute(A,[3,2,1]),3).*ii;

[Stephen23]

+1 neat idea. Requires R2016b or later.

[Andrei Bobrov]

Thank you Stephen!

For old MATLAB ( <= R2016a)

AA = any(bsxfun(@eq,ii,permute(A,[3,2,1])),3).*ii;

Answer 3

[Stephen23]

Without loops, works for any version:

A = [2,2,1,1,1;3,3,3,0,2;5,4,5,0,3]
S = size(A);
C = repmat(1:S(2),S(1),1);
Z = zeros(max(A(:)),S(2));
X = A>0;
Y = sub2ind(size(Z),A(X),C(X));
Z(Y) = A(X)

Giving:

Z =
   0   0   1   1   1
   2   2   0   0   2
   3   3   3   0   3
   0   4   0   0   0
   5   0   5   0   0