randomly shuffle the matrix by taking two rows

For example, if I have

1 5 9 13 17 20

2 6 10 14 18 21

3 7 11 15 19 22

4 8 12 16 20 23

I want to have a function that can shuffle the columns around while keeping the values in the column the same. I want it done by taking two columns together.For example:

9 13 17 20 1 5

10 14 18 21 2 6

11 15 19 22 3 7

12 16 20 23 4 8

In other words, the first two columns were taken together, the next two columns were taken together and randomly mixed in that way.

(Note : My matrix is normally a very large matrix. That's why I wanted to do it with code)

Can you help me to code this?

Thank you.

Answer 1

[Voss]

A = [1     5     9    13    17    20
     2     6    10    14    18    21   
     3     7    11    15    19    22
     4     8    12    16    20    23];

new_idx = randperm(size(A,2)/2)*2-[1; 0]

new_idx = 2×3

5 3 1 6 4 2

A = A(:,new_idx(:)) % A(:,[5 6 3 4 1 2])

A = 4×6

17 20 9 13 1 5 18 21 10 14 2 6 19 22 11 15 3 7 20 23 12 16 4 8

[Berfin Çetinkaya]

I actually didn't want that.

I have a matrix like this:

1 9 8 5 3 9

3 7 7 4 1 10

4 10 6 2 4 9

4 9 7 1 3 5

I want to mix it randomly. But I want it in twos.

Example :

8 5 3 9 1 9

7 4 1 10 3 7

6 2 4 9 4 10

7 1 3 5 4 9

I tried your codes but it didn't give the result I wanted.

[Voss]

It does exactly what you are saying:

A = [1	9	8	5	3	9
     3	7	7	4	1	10
     4	10	6	2	4	9
     4	9	7	1	3	5];
new_idx = randperm(size(A,2)/2)*2-[1; 0];
A = A(:,new_idx(:))

A = 4×6

8 5 3 9 1 9 7 4 1 10 3 7 6 2 4 9 4 10 7 1 3 5 4 9

[Berfin Çetinkaya]

Yes this is exactly what i want. Thank you very much.

[Voss]

You're welcome!