When you create a matrix in the usual way like this,
> a <- matrix(rnorm(10),2,5)> a [,1] [,2] [,3] [,4] [,5] [1,] 1.3488918 0.6225795 -0.7444514 1.3130491 1.7877849 [2,] -0.2385392 0.5656759 0.9037435 -0.2217444 -0.2656875
the dimension dropped after picking up a single row or column in this way,
> b <- a[,1]> b[1] 1.3488918 -0.2385392> dim(b)NULL
The solution is to try it with a parameter drop = FALSE,
> b <- a[,1,drop = FALSE]> b[,1][1,] 1.3488918[2,] -0.2385392> dim(b)[1] 2 1
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