Makes sense if you realize that ?"[" only applies to *vector*,
*list*, and *matrix* indexing and that data frames follow their own
rules that are documented elsewhere ...
So yes, not a bug but I claim it's an infelicity. I might submit a
doc patch.
FWIW
b["A1",]
as.matrix(b)["A1",]
illustrates the difference.
thanks
Ben
On 1/14/22 9:19 PM, Steve Martin wrote:
I don't think this is a bug in the documentation. The help page for
`?[.data.frame` has the following in the last paragraph of the
details:
Both [ and [[ extraction methods partially match row names. By default
neither partially match column names, but [[ will if exact = FALSE
(and with a warning if exact = NA). If you want to exact matching on
row names use match, as in the examples.
The example it refers to is
sw <- swiss[1:5, 1:4] # select a manageable subset
sw["C", ] # partially matches
sw[match("C", row.names(sw)), ] # no exact match
Whether this is good behaviour or not is a different question, but the
documentation seems clear enough (to me, at least).
Best,
Steve
On Fri, 14 Jan 2022 at 20:40, Ben Bolker <bbol...@gmail.com> wrote:
People are often surprised that row-indexing a data frame by [ +
character does partial matching (and annoyed that there is no way to
turn it off:
https://stackoverflow.com/questions/18033501/warning-when-partial-matching-rownames
https://stackoverflow.com/questions/34233235/r-returning-partial-matching-of-row-names
https://stackoverflow.com/questions/70716905/why-does-r-have-inconsistent-behaviors-when-a-non-existent-rowname-is-retrieved
?"[" says:
Character indices can in some circumstances be partially matched
(see ‘pmatch’) to the names or dimnames of the object being
subsetted (but never for subassignment). UNLIKE S (Becker et al_
p. 358), R NEVER USES PARTIAL MATCHING WHEN EXTRACTING BY ‘[’, and
partial matching is not by default used by ‘[[’ (see argument
‘exact’).
(EMPHASIS ADDED).
Looking through the rest of that page, I don't see any other text that
modifies or supersedes that statement.
Is this a documentation bug?
The example given in one of the links above:
b <- as.data.frame(matrix(4:5, ncol = 1, nrow = 2, dimnames =
list(c("A10", "B"), "V1")))
b["A1",] ## 4 (partial matching)
b[rownames(b) == "A1",] ## logical(0)
b["A1", , exact=TRUE] ## unused argument error
b$V1[["A1"]] ## subscript out of bounds error
b$V1["A1"] ## NA
______________________________________________
R-devel@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-devel
--
Dr. Benjamin Bolker
Professor, Mathematics & Statistics and Biology, McMaster University
Director, School of Computational Science and Engineering
(Acting) Graduate chair, Mathematics & Statistics
______________________________________________
R-devel@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-devel
