How to rotate rows of a matrix?

19 views (last 30 days)
I have a matrix A where each row of A has only one value of 1 and the rest are some other number.
A = [9 8 7 1; 9 1 8 7; 9 8 1 7; 9 1 8 7; 9 8 7 1; 1 9 8 7]
How can I rotate all of the rows individually such that the 1 value is in the first column of each row in the resultant matrix? How about the second column? I'd like to do this without a for-loop because I am working with large matrices.
%%% Result:
% First column.
B = [1 9 8 7; 1 8 7 9; 1 7 9 8; 1 8 7 9; 1 9 8 7; 1 9 8 7];
% Second column.
C = [7 1 9 8; 9 1 8 7; 8 1 7 9; 9 1 8 7; 7 1 9 8; 7 1 9 8];

Accepted Answer

Roger Stafford
Roger Stafford on 15 Feb 2017
I think a for-loop is your best bet:
for k = 1:size(A,1)
f = find(A(k,:)==1,1);
A(k,:) = circshift(A(k,:),1-f);
end

More Answers (2)

Image Analyst
Image Analyst on 15 Feb 2017
Try this:
A = [1 0 0 0; 0 1 0 0; 0 0 1 0; 0 1 0 0; 0 0 0 1; 0 0 1 0];
desiredColumn = 1; % or 2 or whatever
output = zeros(size(A)); % Initialize
output(:, desiredColumn) = 1 % Assign desired column to all ones.
  1 Comment
Dominik Mattioli
Dominik Mattioli on 15 Feb 2017
Eek, I edited this just after I posted it, I'm sorry. I forgot to add that the order of each row is important. Do you know how to do that too?

Sign in to comment.


Guillaume
Guillaume on 15 Feb 2017
A version without loop. Not sure it'd be faster than Roger's answer:
destcol = 1; %column where the 1 must be located
[c, r] = find(A' == 1);
A(sub2ind(size(A), repmat(r, 1, size(A, 2)), mod((1:size(A, 2)) + c - 1 - destcol, size(A, 2)) + 1))

Categories

Find more on Operating on Diagonal Matrices in Help Center and File Exchange

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!