swap columns of a matrix

Hello guys/girls

How do i swap columns??

I have this

k_minus =

   -46   -43   -26   -14     7    19    11    32    39    45    45
     0    -4    -7    -7   -44   -44    -7    -7   -15   -15     0

and I want the columns to be in opposite order - How do I do this? and can do this in one go?

Answer 1

[Thomas]

You could also use

 out= fliplr(k_minus)

This flips the matrix left-right http://www.mathworks.com/help/matlab/ref/fliplr.html

[Rasmus]

That is actually easier! :)

Answer 2

[Mischa Kim]

Use

 k_minus_rev = k_minus(:, [length(k_minus(1,:)):-1:1])

[Rasmus]

It totally works, is it possible for you to explain in details what it is that you do?

[Mischa Kim]

Basically, when you do

 k_minus(:,1)

you extract the sub-matrix consisting of all rows in the first column. With

 k_minus(:,[2,1])

you extract all rows of the second, and the first columns, in that order. You can now generalize the last bit

 [length(k_minus(1,:)):-1:1]

to extract all columns ( length(k_minus(1,:)) ), placing the last column first, and the first column last, in descending order ( -1 ).

[Jos (10584)]

You do not need the length statement by using the keyword END:

   MyMatrix_withReversedColumns = MyMatrix(:,end:-1:1)

but I do suggest you stick to FLIPLR. It is the same, but much easier to read!

[kk]

Thank you for this answer! It has helped me "merge" two matrices, i.e. creating a matrix consisting of the first column of matrix A, first column of matrix B, second column of matrix A, second column of matrix B, etc.

Answer 3

[rishabh gupta]

you can also use: k_minus_rev = k_minus(:, [length(k_minus):-1:1])

[Stephen Cobeldick]

The square brackets are totally superfluous, and using end is simpler than using length (of course length should be avoided generally because its output changes depending on the input array size: better to use numel or size with a specific dimension).

So a better (simpler, clearer, less buggy) is exactly as Jos already gave four years ago:

k_minus(:,end:-1:1)

[Helen Joan]

is it possible to do this with a loop?