looking for convenient way to extract matrix from 1*n*n

Hi:

I have a 3*3*3 matrix, and I want to extract the data after its summation.

for example:

A=zeros(5,5,5)
B=sum(A,1);

now B is a 1*5*5 matrix, I want to assign it to a 5*5 matrix C but could not find a way, so looking for help here.

I tried

C=B(1,:,:)

but it does not work.

Thanks!

Answer 1

[Ayush]

Hi YuLi,

You can use squeeze function here:

A=zeros(5,5,5);
size(A) ;%5x5x5
B=sum(A,1);
size(B) %1x5x5
C=squeeze(B);
size(C) %5x5

squeeze function removes all singleton dimensions. You can read more about them here.

It might interest you : Adding extra dimension

Now as, here we are squeezing the dimension, we can also add another dimension to already existing matrix.

A=randi([-10,10],4,4);
size(A) %4x4
C(:,:,2)=C;
size(C) %4x4x2

Hope it helps.

[Yu Li]

thank you.

Answer 2

[David Goodmanson]

Hi YL,

A=zeros(5,5,5)
B=squeeze(sum(A,1));

Squeeze removes all singleton dimensions.

[Yu Li]

David, thank you too.

Answer 3

[Walter Roberson]

A = zeros(5,5,5)

A = 
A(:,:,1) =

     0     0     0     0     0
     0     0     0     0     0
     0     0     0     0     0
     0     0     0     0     0
     0     0     0     0     0


A(:,:,2) =

     0     0     0     0     0
     0     0     0     0     0
     0     0     0     0     0
     0     0     0     0     0
     0     0     0     0     0


A(:,:,3) =

     0     0     0     0     0
     0     0     0     0     0
     0     0     0     0     0
     0     0     0     0     0
     0     0     0     0     0


A(:,:,4) =

     0     0     0     0     0
     0     0     0     0     0
     0     0     0     0     0
     0     0     0     0     0
     0     0     0     0     0


A(:,:,5) =

     0     0     0     0     0
     0     0     0     0     0
     0     0     0     0     0
     0     0     0     0     0
     0     0     0     0     0

B = permute(sum(A,1), [2 3 1]);
size(B)

ans = 1×2

5 5

squeeze() is a convenience function that ends up invoking permute(). squeeze() will not always give you the result you might expect:

C = squeeze(ones(1,1,5)), size(C)

C = 5×1

1 1 1 1 1

ans = 1×2

5 1

Notice that squeeze() removed all of the singular dimensions, not just the first singular dimension.

[Yu Li]

thank you Walter, Ayush's answer come first so I accepted his. but your answer extend my understanding, thank you.