data frame with nested data frame
On Dec 23, 2010, at 5:06 PM, Vadim Ogranovich wrote:
Dear R-users, I am somewhat puzzled by how R treats data frames with nested data frames.
Speaking as a fellow user, .... why? Why would we want dataframes inside dataframes? Why wouldn't lists of dataframes be more appropriate if you were hoping to use apply or <some other function> ?
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)
cbind.data.frame (dispatched if the first argument to cbind is a dataframe) would give you another dataframe without the mess of having nesting. > cbind(z, b=2) x b 1 1 2 This is also the time to ask .... what is it that you are _really_ trying to accomplish?
## 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"
Yes. the second one is equivalent to passing just the list portions of the nameless data.frame and ignoring attributes.
## 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'
That is a puzzle, I agree.
This succeeds:
z <- data.frame(x=1, y=2)
rbind(z,z
#########
x y
1 1 2
2 1 2
Perhaps a bug (... trying to add drop=FALSE had an amusing result:
> rbind(z,z, drop=FALSE)
x
1 1
2 1
drop 0
--
David
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
David Winsemius, MD West Hartford, CT > sessionInfo() R version 2.12.1 (2010-12-16) Platform: x86_64-apple-darwin9.8.0/x86_64 (64-bit) locale: [1] en_US.UTF-8/en_US.UTF-8/C/C/en_US.UTF-8/en_US.UTF-8 attached base packages: [1] splines stats graphics grDevices utils datasets methods base other attached packages: [1] sos_1.3-0 brew_1.0-4 lattice_0.19-13 loaded via a namespace (and not attached): [1] grid_2.12.1 tools_2.12.1