Select matrix column (resp. row) as Nx1 (resp. 1xD) matrix, as opposed to vector

Question

Let X be an N by D matrix. Selecting a submatrix of size n by d returns a matrix of those dimensions unl

Answer 1

If you don't want to simplify matrix subsets to vectors just tell [ not to drop dimensions:

> dim(X[1:2,1, drop=FALSE])
[1] 2 1
> dim(X[1,1:2, drop=FALSE])
[1] 1 2

See ?"[" for details.