Hi Austin,

What version of R are you using? It works for me for R 2.10.0 Patched on Win
XP Pro:

R> a <- matrix(c(1, 2, 3, 4), nrow = 2)
R> a
# [1] 1 3
# [2] 2 4
R> rmask <- c(TRUE, FALSE)
R> a[rmask,]
# [1] 1 3

HTH,
Jorge


On Fri, Dec 4, 2009 at 3:52 PM, Austin Huang <> wrote:

> One problem I've been having is the special case in which only one
> row/column remains and the variable gets converted into a vector when
> entries are removed by logical masking. This is a problem because
> subsequent
> code may rely on matrix operations (apply, colsums, dim, etc) For example:
>
> > a <- matrix(c(1, 2, 3, 4), nrow = 2)
> > a
>     [,1] [,2]
> [1,]    1    3
> [2,]    2    4
> > rmask <- c(TRUE, FALSE)
> > b <- a[rmask, ]
> > colSums(b)
> Error in colSums(b) : 'x' must be an array of at least two dimensions
>
> To ensure the code works regardless of how the matrix gets modified, I need
> to explicitly recast results to a matrix, for example:
>
> b <- matrix(a[rmask, ], ncol = 2)
>
> This can get messy, requiring extra work to maintain column/row names or
> additional commands to determine the correct dimensions of the matrix (for
> example, if I'm masking both rows and columns simultaneously). Is there a
> more elegant way to deal with this in R?
>
> ~A
>
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