(following up on myself:)
>>>>> "MM" == Martin Maechler
<maechler@stat.math.ethz.ch> writes:
MM> In R and S, the general idea is that data.frames
MM> must have unique row.names (aka dimnames(.)[[1]]).
MM> Several observations / problems (in R *and* S !).
....
MM> 2)
MM> Now, in S (but not in R),
MM> the "row.names<-" function
MM> gives an error if you try to assign non-unique row.names.
MM> This is as desired (and R should do the same).
MM> (== BUG REPORT for R )
this is easily fixed in data.frame.R if one doesn't want to do the fix
for "3)" as well.
MM> 3) However, I can still (both in S-plus 3.4 & 5.0r2)
MM> do
MM> attr(dat, "row.names") <- <nonunique character>
MM> and get a resulting data.frame dat with non-unique row.names.
MM> PROPOSITION 2: I think I want to make sure that a(the same?)
MM> error message as in "2)" is generated in this case.
MM> (this is relatively easily accomplished via R's
MM> SetAttrib() in src/main/attrib.c)
MM> ------------------------------------------------------------------
>>>>> or am I completely wrong, and there should be a way you
can
>>>>> construct a data.frame with non-unique row.names ???
MM> ------------------------------------------------------------------
It seems I am wrong -- at least in the eyes of Mathsoft's S-plus 5
writers:
data.frame() in S-plus 5.0r2's has a new argument
dup.names.ok = F
which you can set to TRUE in order to construct data.frames with non-unique
row.names.
Note however that John Chamber's S version 4 (which underlies S-plus 5)
does NOT have such an argument.
---
Currently,
I tend to conclude that we should follow S-plus 5 here,
and allow non-unique row.names , however only via the low-level
attr(. "row.names")
and not via row.names(.) <- ...
Further: the 'dup.names.ok = FALSE' seems a good idea for data.frame()
when you want to speed up constructing of huge data.frames...
(e.g. when using read.table(.) on large files !!).
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