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
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