reducing matrices under certain conditions

Question

M is a matrix 4x2000000 composed of several submatrix Ai such that Ai(1:3,j) is the same vector for j = 1,...,size(Ai,2

Answer 1

One approach -

[~,~,idx] = unique(M(1:3,:)','rows')  %//'
valid = ismember(M(4,:),V)
valid_idx = accumarray(idx(valid),M(4,valid).',[],@(x) ...
                                 numel(unique(x)))>=numel(V) %//'
out = M(:,ismember(idx,find(valid_idx)))