Determining if any duplicate rows in two matrices in MatLab -


introduction problem:

i'm modelling system have matrix x=([0,0,0];[0,1,0],...) each row represent point in 3d-space. choose random row, r, , take following rows , rotate around point represented r, , make new matrix these rows, x_rot. want check whether of rows x_rot equal 2 of rows of x (i.e. 2 vertices on top of each other), , if case refuse rotation , try again.

actual question:

until have used following code:

x_sim=[x;x_rot]; if numel(unique(x_sim,'rows'))==numel(x_sim);     x(r+1:n+1,:,:)=x_rot; end

which works, takes on 50% of running time , considering if in here knew more efficient way it, since don't need information unique.

p.s. if matters typically have between 100 , 1000 rows in x.

best regards, morten

additional: x-matrix contains n+1 rows , have 12 different rotational operations can apply sub-matrix x_rot:

step=ceil(rand()*n); r=ceil(rand()*12); x_rot=x(step+1:n+1,:); x_rot=bsxfun(@minus,x_rot,x(step,:)); x_rot=x_rot*rot(:,:,:,r); x_rot=bsxfun(@plus,x_rot,x(step,:));

two possible approaches (i don't know if faster using unique):

  1. use pdist2:

    d = pdist2(x, x_rot, 'hamming'); %// 0 if rows equal, 1 if different. %// distance function do, try available , choose fastest result = any(d(:)==0);

  2. use bsxfun:

    d = squeeze(any(bsxfun(@ne, x, permute(x_rot, [3 2 1])), 2)); result = any(d(:)==0);

result 1 if there row of x equal row of x_rot, , 0 otherwise.


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