[Rd] data.matrix returns mode logical for zero rows (PR#8496)

[jonathan.swinton@astrazeneca.com]

Full_Name: Jonathan Swinton
Version: 2.2.1
OS: Windows
Submission from: (NULL) (193.132.159.169)


#The first line of description for data.matrix says that it will
#	'Return the matrix obtained by converting all the variables in a
#    data frame to numeric mode and then binding them together as the
#     columns of a matrix.'

#However when called with a data.frame with zero rows, data.matrix returns a
matrix 
#of mode logical rather than numeric. This conflicts with the documentation
#and is not what seems sensible.

# One underlying reason for this is that when a zero-length column of a matrix
of mode logical is 
# asserted to be numeric the matrix is not actually cast to numeric. I wonder if
that too is a bug?

> R.version.string
[1] "R version 2.2.1, 2005-12-20"
> df <- data.frame(matrix(1:2,nrow=2))
> mode(data.matrix(df)[,1])
[1] "numeric"
> mode(data.matrix(df[FALSE,])[,1])
[1] "numeric"
> 
> # Underlying cause
> x <- matrix(nr = 2,nc = 1 )
> mode(x)
[1] "logical"
> x[, 1] <-   c(1,2)
> mode(x)
[1] "numeric"
> 
> x0 <- matrix(nr = 0, nc = 1)
> x0[, 1] <-   numeric(0)
> mode(x0)
[1] "logical"
> mode(x0[,1])
[1] "logical"