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I have a matrix for which each row has 12 elements that represent the xyz coordinates of 4 points. So each row of M is (x1,y1,z1,x2,y2,z2,x3,y3,z3,x4,y4,z4). Some points have NA as z values. I want another matrix to be the same as M but with the coordinates of those points with z=NA placed last. For ezample if z1=NA then the new matrix row should be (x2,y2,z2,x3,y3,z3,x4,y4,z4,x1,y1,z1)