This is documented behavior. From ?"[.data.frame":
Both ‘[’ and ‘[[’ extraction methods partially match row
names. By default neither partially match column names, but
‘[[’ will unless ‘exact=TRUE’. If you want to do exact
matching on row names use ‘match’ as in the examples.
In the history of S, S-PLUS and R partial matching for subscripts and
indices has been used in many places, but over time it has been removed
from some. Some methods for "[[" have an "exact" argument that allows
specification of whether you want exact or prefix matches. However, as
the docs indicate, this doesn't apply to "[" for rownames in data
frames. At this point, the behavior is unlikely to change -- it risks
breaking too much old code (that's just my opinion based on observation
of the evolution of R -- I have no control over that evolution). Follow
the suggestion in the help for [.data.frame to get exact matching.
-- Tony Plate
Yurii Aulchenko wrote:
Dear all,
sorry to bother you with potentially known issue --
we have noticed that if we select data frame rows by rownames, we get
some results back if the match can be done unambiguously, though the
match is not perfect (see example), e.g. x{"2",] will return a row if
there is a unique row with name starting with "2" (but may be "2375745"!)
is that a planned behavior of R which will be maintained? for us it
was a bit unexpected...
Yurii
-----------------------------
> a <- data.frame(x=1:3, y=1:3)
> rownames(a) <- c("2535","59617","555")
> a
x y
2535 1 1
59617 2 2
555 3 3
> a["5",]
x y
NA NA NA
> a["555",]
x y
555 3 3
> a["2",]
x y
2535 1 1
> version
_
platform i386-apple-darwin9.8.0
arch i386
os darwin9.8.0
system i386, darwin9.8.0
status Under development (unstable)
major 2
minor 11.0
year 2009
month 12
day 07
svn rev 50688
language R
version.string R version 2.11.0 Under development (unstable)
(2009-12-07 r50688)
-----------------------------------------------------------
Yurii Aulchenko
Erasmus MC Rotterdam
Department of Epidemiology, Ee 2200
Postbus 2040, 3000 CA Rotterdam
The Netherlands
phone: +31107043486
fax: +31107044657
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