[R] data frame with nested data frame

[Vadim Ogranovich]

Dear R-users,

I am somewhat puzzled by how R treats data frames with nested data frames. Below are a couple of examples, maybe someone could help explain what the guiding logic here is.

## construct plain data frame
> z <- data.frame(x=1)

## add a data frame member
> z$y <- data.frame(a=1,b=2)

## puzzle 1: z is apparently different from a straightforward construction of the 'same' object
> all.equal(z, data.frame(x=1,y=data.frame(a=1,b=2)))
[1] "Names: 1 string mismatch"                                                       "Length mismatch: comparison on first 2 components"
[3] "Component 2: Modes: list, numeric"                                              "Component 2: names for target but not for current"
[5] "Component 2: Attributes: < Modes: list, NULL >"                                 "Component 2: Attributes: < names for target but not for current >"
[7] "Component 2: Attributes: < Length mismatch: comparison on first 0 components >" "Component 2: Length mismatch: comparison on first 1 components"

## puzzle 2: could not rbind z
> rbind.data.frame(z, z)
Error in `row.names<-.data.frame`(`*tmp*`, value = c("1", "1")) :
  duplicate 'row.names' are not allowed
In addition: Warning message:
non-unique value when setting 'row.names': '1'

> version
               _
platform       i386-pc-mingw32
arch           i386
os             mingw32
system         i386, mingw32
status
major          2
minor          9.1
year           2009
month          06
day            26
svn rev        48839
language       R
version.string R version 2.9.1 (2009-06-26)


Thanks,
Vadim

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