How can I combine three 2D matrices into a 3D matrix?

Question

a = [1 2 3;
     4 5 6;
     7 8 9];

b = [10 11 12;
     13 14 15;
     16 17 18;
    ];

c = [19 20 21;
     22 23 24;
     25 26 27;
    ];

I want to combine the above 2D matrices into a 3D matrix mat so that I can access them in the following way,

>> mat(:, :, 1)
ans = 
[1 2 3
 4 5 6
 7 8 9]

>> mat(:, :, 2) 
ans = 
[10 11 12
 13 14 15
 16 17 18]

>> mat(:,:,3)
ans = 
[19 20 21
 22 23 24
 25 26 27]

I tried the following,

mat = [a, b, c];

But, it actually doesn't work.

So, how can I achieve that?

In addition to the answers read the documentation associated with `cat` to get more ideas of ways to combine things. — Matt, Jul 12 '17 at 19:57
@hbaderts: Hmm, wonder why that didn't show up on the "Related" sidebar. — gnovice, Jul 12 '17 at 20:14

gnovice · Answer 1 · 2017-07-12T20:05:16.847

5

Square brackets [] are for horizontal and vertical concatenation of matrices. You can use the cat function for concatenating along higher dimensions:

mat = cat(3, a, b, c);

More info can be found here.

edited Jul 12 '17 at 20:05

answered Jul 12 '17 at 19:55

gnovice

125,304
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what is wrong with `m7913d`'s answer? – user366312 Jul 12 '17 at 20:06
@anonymous: Nothing. That's just another way to achieve the same thing. – gnovice Jul 12 '17 at 20:06
@anonymous This is a nice alternative, shorter, but somewhat harder to remember. – m7913d Jul 12 '17 at 20:14

score 3 · Accepted Answer · answered Jul 12 '17 at 19:54

3

You can do it as follows using explicit matrix indexing:

mat(:,:,1) = a;
mat(:,:,2) = b;
mat(:,:,3) = c;

mat = [a, b, c]; will create a 3x9 matrix.

answered Jul 12 '17 at 19:54

m7913d

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How can I combine three 2D matrices into a 3D matrix?

2 Answers2