## Switch columns in a matrix without a loop

### yakov (view profile)

on 13 Apr 2013
Latest activity Commented on by sami elahj

### sami elahj (view profile)

on 10 Jan 2016
How can I switch specific columns in a matrix (for example every 4th column), in one command without using a loop? Is it even possible?

### Florian (view profile)

on 13 Apr 2013

Hi Yakov,
please specify, since in a matrix with 10 columns you will have for 3 columns at index 3,6,9 but only 2 columns with index mod 5, namely 5, 10.
Hence could you please specify exactly which columns you want to switch. Or do you want to mix all columns randomly?
Regards, Florian

yakov

### yakov (view profile)

on 13 Apr 2013
Hi Florian, for example, if I choose to switch every third column, in a matrix of 10 columns I'd want to switch the 3,6,9 columns only, and if I choose to switch every fourth column I'd want to switch the 4 and 8 columns. I want to switch them with a different column vector of my choosing, but all of them with the same vector.

### Ahmed A. Selman (view profile)

on 13 Apr 2013

for exchanging two columns 3 - 9 :
A = randi(20,4,10); % A random 4 by 10 matrix of integers
A(1,:)=[1 2 3 4 5 6 7 8 9 10]; % the first row only is replaced for clarity
B=A; % the new matrix, same as A for now
B(:,3)=A(:,9); % puts 3 of B with 9 of A
B(:,9)=A(:,3); % puts 9 B with 3 A
B has columns 3 and 9 exchanged with A 9 and 3, and A is intact. A similar method to exchange columns 3 - 6 - 9 - 3. So if you want to use same A, use A=B.
To exchange rows use B(row_no,:)=A(new_row,:)..etc

sami elahj

on 10 Jan 2016
thanx