# How to switch two values in a matrix?

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Changoleon on 16 Nov 2016
Commented: Changoleon on 17 Nov 2016
Hi. I have a matrix :
x = [ 6.5 7 23 24 25]
x =
6.5000 7.0000 23.0000 24.0000 25.0000
However, the numbers inside matrix x are not in the correct spots. I need to move some of them. In order to find out which ones to move, I have to look at another matrix which is called c and c equals to:
c = [ 1 2 3 4 5 ;
3 2 4 1 5]
c =
1 2 3 4 5
3 2 4 1 5
I want to write a code which can detect which columns in matrix c do not have the same numbers in its two rows. For example in matrix c the answer is 1st, 3rd, and 4th columns. Following is what I have done.
y = find(c(1,:)~=c(2,:));
Now this line of code helps me to find where in numbers do not match.
Now I want a code which can apply the findings of y to swap the values in matrix x.
In other words, the out put of the code that I am looking for should give me
J = blahblah(x);
J = [ 24 7 6.5 23 25];
This is very important and I have no clue how to do it.
Any help would be appreciated.

Roger Stafford on 16 Nov 2016
If I understand the method in your example correctly, then using your definition of x and c, the following should accomplish the necessary transformation using matlab's 'circshift' function:
y = find(c(:,1)~=c(2,:));
J = x;
J(y) = J(circshift(y,1));
Roger Stafford on 17 Nov 2016
@Changoleon. Try this:
y = find(c(:,1)~=c(2,:));
J = x;
J(y) = J(circshift(y,1,2));
The '2' specifies that shifting is along the 2nd dimension (along the row)
Changoleon on 17 Nov 2016
Thanks! You're the best

Walter Roberson on 16 Nov 2016
If you have two indices, I, J, at which you need to swap, then
YourMatrix([I, J]) = YourMatrix([J, I]);
will do the swap.
If you indices are expressed through a row vector of length 2, y, then
YourMatrix(y) = YourMatrix(fliplr(y));
Use flipud if it is a row vector.
This will not work as well with length greater than 2: if your vector were an odd length then one of the elements would be set to itself.
Changoleon on 16 Nov 2016
As you said the values that I want to change could be more than 2. Up to 75. The method should be all automated. How can I do that?
Walter Roberson on 16 Nov 2016
The question becomes how to match the source and destination.
The general syntax
YourMatrix(ListOfDestiantions) = Yourmatrix(ListOfCorrespodingSources);
reads everything from Yourmatrix(ListOfCorrespodingSources) before doing any assignments at YourMatrix(ListOfDestiantions), so it is safer than using
for K = 1 : length(ListOfCorrespodingSources)
YourMatrix(ListOfDestinations(K)) = YourMatrix(ListOfCorrespodingSources(K));
end
The "for" version of it messes up on swapping values.