How can I combine every Nth row of a matrix into a new matrix using a loop?

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Jane 2012-10-5

评论： Walter Roberson 2020-5-10

I have a huge matrix A:

A=[X,Y]

and would like to create a new matrix B using every Nth row of A:

B=[A(1,:); A((1+N),:); A((1+2N),:); ...; A((1+(length(X)-N)),:)]

where length(X)>>1000.

How can I create this new matrix B using a loop?

Thomas 2012-10-5

编辑：Thomas 2012-10-5

Is this what you want? You do not need to use loops

 % initial data
a=[1:10;11:20]' 
 % select  every 3rd row
 out = a(1:3:end,:)

If i need to go through a for loop how am i going to do it?

Thank you!

Walter Roberson 2020-5-10

r__r_ = ceil(size(A,1)/N);
B = zeros(r__r_, size(A,2), 'like', A);
for r__r__ = 1 : r__r_
    B(r__r__,:) = A(1 - N + r__r__*N, :);
end

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