[Rd] Strange behaviour of the [[ operator
Peter Dalgaard
p.dalgaard at biostat.ku.dk
Sat Sep 30 19:00:50 CEST 2006
Seth Falcon <sfalcon at fhcrc.org> writes:
> > Similar things happen in many similar circumstances.
>
> Here's a similar thing:
Not really, no?
> > v <- 1:5
> > v
> [1] 1 2 3 4 5
> > v[mustBeDocumentedSomewhere=3]
> [1] 3
>
> And this can be confusing if one thinks that subsetting is really a
> function and behaves like other R functions w.r.t. to treatment of
> named arguments:
>
> > m <- matrix(1:4, nrow=2)
> > m
> [,1] [,2]
> [1,] 1 3
> [2,] 2 4
> > m[j=2]
> [1] 2
Or even
> m[j=2,i=]
[1] 2 4
However, what would the argument names be in the >2-dim case? i, j are
used only in help("[") and that page is quite specific about
explaining that named matching doesn't work.
--
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