Reshaping a matrix and binding two values together

Hello dear Matlab Community!

Since I am a total novice in Matlab I'm stuck with the following, probably easily solvable, problem.

I have a matrix in the following arrangement:

20 9

12 4

3 15

6 7

. .

. .

and so forth, the integers of each column reach from 1 to 20 and are paired with an integer from the other column. The same integers cannot be paired, so for example 14 14 would be impossible.

I want to present randomized pairings of stimuli.

So, firstly I need to rearrange my two columns to this from: 20 9 12 4 3 15 6 7...

Does anybody know how to do this?

And secondly, I want to bind every 2 integers and then shuffle them. For example, 20 and 9 are bound, 12 and 4 are bound, 3 and 15 are bound and so forth. And then shuffle them, so a new arrangement might be: 12 4 20 9 3 15...

I would very much appreciate any help!

Thanks in advance and best Regards!

Answer 1

[KSSV]

iwant =  reshape(randperm(20),10,2) ;

[Rupert Steinmeier]

This gives me two ten-digit colums containing the numbers 1 to 20 and I don't see how that helps me. But thanks for the answer!

[KSSV]

If A is your m*2 matrix

A = A' ; 
iwant = A(:)'

Is this what you want?

[Rupert Steinmeier]

Yes! Thank you very much! :)

This is the answer to my first question.

Do you also know how to bind 2 integers together in order to shuffle the pairings?

Anyway, many thanks for your effort!

[KSSV]

My first answer helps for this.

A = rand(10,2) ; 
A = A' ; 
A = A(:)' ; 
idx =  reshape(randperm(length(A)),10,2) ;
A = A(idx)

[Rupert Steinmeier]

I get the row I want using this "A = A' ; A = A(:)' ;"

But when I try "idx = reshape(randperm(length(A)),10,2)", I get the following error: "Error using reshape

Number of elements must not change. Use [] as one of the size inputs to automatically calculate the appropriate size for that dimension."

[KSSV]

idx =  reshape(randperm(length(A)),[],2) ;

It seems you have more than 20 elements....

[Rupert Steinmeier]

Yeah, when I do this "A = A' ; A = A(:)' ;", I have my integers listed in a 40-digit row.

So, from this:

12 20

9 4

2 17

. .

. .

to this:

12 20 9 4 2 17...

Which is exactly what I wanted!

But now, I want to bind 12 and 20 together as well as 9 and 4, 2 and 17 and so forth.

And then shuffle the row. One possible outcome would be 9 4 2 17 12 20....

Do you know, what I mean?

[KSSV]

Read about randperm.