How to select a specific column in matrices?

I have four (4x4) matrices A B C D. I need to put all the second colums of the four matrices in another matrix X. I tried using

xdatatemp = xdata(:,[end 2]); X = xdatatemp

but it shows an error. Thank you in advance!

Answer 1

[Star Strider]

Concatenate them, then select the second column of the concatenated matrix —

A = randi(9,4)

A = 4×4

7 1 8 5 2 4 5 3 8 6 1 5 1 8 4 4

B = randi(9,4)

B = 4×4

7 9 2 5 3 8 9 8 1 4 9 1 9 5 9 6

C = randi(9,4)

C = 4×4

5 3 4 2 2 7 7 1 4 8 2 3 2 3 9 9

D = randi(9,4)

D = 4×4

5 1 3 7 8 8 7 5 3 1 1 4 1 7 2 1

ABCD = cat(3,A,B,C,D)

ABCD = 
ABCD(:,:,1) =

     7     1     8     5
     2     4     5     3
     8     6     1     5
     1     8     4     4


ABCD(:,:,2) =

     7     9     2     5
     3     8     9     8
     1     4     9     1
     9     5     9     6


ABCD(:,:,3) =

     5     3     4     2
     2     7     7     1
     4     8     2     3
     2     3     9     9


ABCD(:,:,4) =

     5     1     3     7
     8     8     7     5
     3     1     1     4
     1     7     2     1

NewMatrix = squeeze(ABCD(:,2,:))                                % Elimiinate Singleton Dimensions with 'squeeze'

NewMatrix = 4×4

1 9 3 1 4 8 7 8 6 4 8 1 8 5 3 7

.

[Ara Guz]

Hi, where did you get (9,4)?

[Ara Guz]

how about if i need the second row instead of a column, do i change it as

NewMatrix = squeeze(ABCD(2,:,:))?

[Star Strider]

To get the second row simply requires changing the addressing slightly from:

NewMatrix = squeeze(ABCD(:,2,:))                                % Elimiinate Singleton Dimensions with 'squeeze'

to:

NewMatrix = squeeze(ABCD(2,:,:)).'                              % Elimiinate Singleton Dimensions with 'squeeze'

Note the added transposition.

Running tthe code with that change:

A = randi(9,4)

A = 4×4

3 4 4 6 9 7 6 9 4 6 5 1 4 4 8 1

B = randi(9,4)

B = 4×4

7 8 9 7 8 4 3 7 2 9 4 8 2 1 2 9

C = randi(9,4)

C = 4×4

6 9 2 9 7 8 8 9 4 5 8 5 6 3 2 8

D = randi(9,4)

D = 4×4

9 4 8 3 9 9 3 4 6 9 1 6 4 1 2 6

ABCD = cat(3,A,B,C,D)

ABCD = 
ABCD(:,:,1) =

     3     4     4     6
     9     7     6     9
     4     6     5     1
     4     4     8     1


ABCD(:,:,2) =

     7     8     9     7
     8     4     3     7
     2     9     4     8
     2     1     2     9


ABCD(:,:,3) =

     6     9     2     9
     7     8     8     9
     4     5     8     5
     6     3     2     8


ABCD(:,:,4) =

     9     4     8     3
     9     9     3     4
     6     9     1     6
     4     1     2     6

NewMatrix = squeeze(ABCD(2,:,:)).'                              % Elimiinate Singleton Dimensions with 'squeeze'

NewMatrix = 4×4

9 7 6 9 8 4 3 7 7 8 8 9 9 9 3 4

.

Answer 2

[Monika Jaskolka]

A = ones(4)

A = 4×4

1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

B = ones(4)*2

B = 4×4

2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2

C = ones(4)*3

C = 4×4

3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3

D = ones(4)*4

D = 4×4

4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4

X = [A(:,2), B(:,2), C(:,2), D(:,2)]

X = 4×4

1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4