xtabs to dataframe fails (PR#3754)
daniel.frey@switzerland.org wrote:
Full_Name: Daniel Frey Version: 1.7.1 OS: Windows 2000 Submission from: (NULL) (80.254.164.242) Generating a data frame out of a xtabs result acts unusual. Take the following sample to reproduce it:
> a.a <- c("a","a","a","b","b")
> a.b <- c("c","c","d","e","f")
> a.df <- data.frame(list("A"=a.a,"B"=a.b))
> a.x <- xtabs(~A+B,a.df)
> a.x
B
A c d e f
a 2 1 0 0
b 0 0 1 1
> data.frame(a.x)
A B Freq
1 a c 2
2 b c 0
3 a d 1
4 b d 0
5 a e 0
6 b e 1
7 a f 0
8 b f 1
I would expect something like a.x itself. Instead I have to give the exact
bounds, otherwise it doesn't convert properly:
> data.frame(a.x[1:2,1:4])
c d e f
a 2 1 0 0
b 0 0 1 1
I consider this a bug, as consistency of the handling breaks here.
Daniel Frey
a) data.frame() calls as.data.frame()
b) as.data.frame() uses its method as.data.frame.table(), because
class(a.x)
[1] "xtabs" "table"
c) ?as.data.frame.table tells us:
`as.data.frame.table' is a method for the generic function
`as.data.frame' to convert the array-based representation of a
contingency table to a data frame containing the classifying
factors and the corresponding counts (the latter as component
`Freq'). This is the inverse of `xtabs'.
So, what is the bug?
I guess you expect something like
data.frame(unclass(a.x))
Uwe Ligges