how to find index from matrix in another matrix?

Hi all,

I have two different 3d matrices (A=72*46*2192) and (B=72*46*2192), in which I want to find the indices equal to 4 and 5 from A in B.

The result should be a 3d matrix as well, not linear indices.

Any help would be appreciated.

[David Hill]

I do not understand your question. A simple example might help.

[Lilya]

Thanks for your responce David.

A = rand(2,3,4);

B=rand(2,3,4);

Matrix A should have elements = 4 and 5.

I want to use the index of those 4 and 5 in A to find the corresponding elements in B.

Answer 1

[Fangjun Jiang]

%C is the logical index matrix.

A=zeros(2,3,4);
A(:,:,4)=4;
A(:,3,4)=5;
C=or(A==4,A==5)

C = 2×3×4 logical array
C(:,:,1) =

   0   0   0
   0   0   0


C(:,:,2) =

   0   0   0
   0   0   0


C(:,:,3) =

   0   0   0
   0   0   0


C(:,:,4) =

   1   1   1
   1   1   1

%To use it to select corresponding elements in B

B=rand(2,3,4);
B_select=B(C)

B_select = 6×1

0.2953 0.0888 0.5716 0.4577 0.5288 0.3675

LinearIndex=find(C);
[SubX,SubY,SubZ]=ind2sub(size(C),LinearIndex)

SubX = 6×1

1 2 1 2 1 2

SubY = 6×1

1 1 2 2 3 3

SubZ = 6×1

4 4 4 4 4 4

[Lilya]

Thank you so much.

but how can i return the index to matrix B?

not a linear result

[Fangjun Jiang]

See the updated answer to understand

1. Logical index
2. Linear index
3. Subscript index