There looks to be a bug in do_attr() (src/main/attrib.c): incorrect
partial matches of attribute names can be returned when there are an odd
number of partial matches.
E.g.:
> x <- c(a=1,b=2)
> attr(x, "abcdef") <- 99
> attr(x, "ab")
[1] 99
> attr(x, "abc") <- 100
> attr(x, "ab") # correctly returns NULL because of ambig partial match
NULL
> attr(x, "abcd") <- 101
> attr(x, "ab") # incorrectly returns non-NULL for ambig partial match
[1] 101
> names(attributes(x))
[1] "names" "abcdef" "abc" "abcd"
>
The problem in do_attr() looks to be that after match is set to
PARTIAL2, it can be set back to PARTIAL again. I think a simple fix is
to add a "break" in this block in do_attr():
else if (match == PARTIAL) {
/* this match is partial and we already have a partial match,
so the query is ambiguous and we return R_NilValue */
match = PARTIAL2;
break; /* <---- ADD BREAK HERE */
} else {
However, if this is indeed a bug, would this be a good opportunity to
get rid of partial matching on attribute names -- it was broken anyway
-- so toss it out? :-) Does anyone depend on partial matching for
attribute names? My view is that it's one of those things like partial
matching of list and vector element names that seemed like a good idea
at first, but turns out to be more trouble than it's worth.
On a related topic, partial matching does not seem to work for the
"names" attribute (which I would regard as a good thing :-). However,
I'm puzzled why it doesn't work, because the code in do_attr() seems to
try hard to make it work. Can anybody explain why?
E.g.:
> attr(x, "names")
[1] "a" "b"
> attr(x, "nam")
NULL
> sessionInfo()
R version 2.4.1 (2006-12-18)
i386-pc-mingw32
locale:
LC_COLLATE=English_United States.1252;LC_CTYPE=English_United
States.1252;LC_MONETARY=English_United
States.1252;LC_NUMERIC=C;LC_TIME=English_United States.1252
attached base packages:
[1] "stats" "graphics" "grDevices" "utils" "datasets" "methods"
[7] "base"
>
-- Tony Plate
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