[R] data.frame to matrix

[Duncan Murdoch]

On Mon, 9 Feb 2004 17:47:36 -0300, "Gustavo Pinheiro"
<gustavo at estatcamp.com.br> wrote :

>Hello all,
>
>I've had trouble converting a data.frame to a matrix (numeric) using either
>data.matrix() and as.matrix().
>After executing one of those I end up with another data.frame with only the
>first column of the original data.frame.
>I use a window (tcltk) to let the user choose the columns he wants and then
>I retrieve them using the following:
>
>varstemp <- .numeric[as.numeric(tkcurselection(subgroupsBox)) + 1]
>
>where ".numeric" is the original (complete) data.frame.
>
>Any ideas why is this happening? I'm using R1.8.1 in WinXP by the way.

I'd guess "as.numeric(tkcurselection(subgroupsBox)) + 1" isn't
returning what you think it's returning, or maybe .numeric isn't in
the form you think.

I'd also recommend using both row and column indices when working with
data frames.  What you have selects columns from a data.frame, but not
from a matrix (assuming that the index is a vector of integers).  I
find it's safer to treat data.frames as matrices whenever you can,
i.e. use a blank row index

varstemp <- .numeric[ , as.numeric(tkcurselection(subgroupsBox)) + 1] 

Duncan Murdoch