Simple reformat data question

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Rahul
Rahul 2012-4-5
I have
a=[1:16]
and I need to get
b= 1 2 4 3
5 6 8 7
13 14 16 15
9 10 12 11
have a number of such vectors that I want to convert into this format..

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采纳的回答

Thomas
Thomas 2012-4-5
There might be a shorter way of doing this but this is a start..
a=[1:16]
b=reshape(a,4,[])'
c=b(:,3)
b(:,3)=[]
b=[b c]
d=b(3,:)
b(3,:)=[]
b=[b;d]

更多回答（2 个）

Sean de Wolski
Sean de Wolski 2012-4-5
If you can explain what's going on we might be able to help you with a more general solution. Otherwise, there doesn't appear to be a pattern and the solution is thus:
b = a([1 2 4 3; 5 6 8 7; 13 14 16 15;9 10 12 11])
More per comments
A=reshape(1:16,4,4)'
B = A;
B([end-1 end],:) = B([end end-1],:);
B(:,[end-1 end]) = B(:,[end end-1]);
  2 个评论
Rahul
Rahul 2012-4-5
I have to exchange the last and second last row and last and second last column. This is ok for the example matrix, but I have a number of such vectors that I need to reformat.. I'm trying the above solution by Thomas..

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Matt Tearle
Matt Tearle 2012-4-5
How much does this need to generalize? If a might be very long, using a transpose is inefficient. Will the number of elements of a be fixed? If not, will the number of elements of a always be a square (so it can be reshaped into an n-by-n matrix)?
If numel(a) can be large, but will always be square:
A = 1:49; % or whatever
n2 = length(A);
n = sqrt(n2);
idx = mod(0:n:(n*n2-1),n2-1)+1;
B = reshape(A(idx),n,n);
B(n,n) = n2;
B([end-1 end],:) = B([end end-1],:);
B(:,[end-1 end]) = B(:,[end end-1]);

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