Hi, Use `drop=FALSE`. ?b<- matrix(c(2,1,-1,-2),ncol=1) ?b[1:3,1] #[1]? 2? 1 -1 ?b[1:3,1,drop=FALSE] #or b[1:3,,drop=FALSE] #???? [,1] #[1,]??? 2 #[2,]??? 1 #[3,]?? -1 A.K. hi all, i got a small question tonight.> matrix(b,4)[]? ? ?[,1] [1,] ? ?2 [2,] ? ?1 [3,] ? -1 [4,] ? -2> dim(matrix(betan,4))[1] 4 1 As shown, b is a 4X1 matrix.> matrix(betan,4)[1:3,1][1] ?2 ?1 -1 However, I think the result should be ? ? ?[,1] [1,] ? ?2 [2,] ? ?1 [3,] ? -1 How could I get the result above? Many thanks,