eliminating some elements randomly from a matrix

Suppose that I have a Matrix A and I want to eliminate k elements randomly from each column (1<=k<size(A,1))

so the remaining matrix, A' , would have the size equal to:

size(A',1)=size(A,1)-k,  size(A',2)=size(A,2)

How can I do this? Thank you.

Answer 1

[Honglei Chen]

A = magic(5)
k = 2;
[M,N] = size(A);
ridx = zeros(k,N);
for m = 1:N
    ridx(:,m) = randperm(M,k);
end
cidx = repmat(1:N,k,1);
B = A;
B(sub2ind([M N],ridx(:),cidx(:)))=[];
reshape(B,M-k,[])