[R] Matrix dimnames
Michael Prager
mike.prager at noaa.gov
Thu Nov 2 02:12:49 CET 2006
Daniel Gatti wrote:
> How does one assign names to the columns of a matrix so that the columns
> can be accesses using the '$' operator? It seem that x$c1 below should
> return column 1.
>
> > x = matrix(1:4,2)
> > dimnames(x) = list(c("r1", "r2"), c("c1", "c2"))
> > x
> c1 c2
> r1 1 3
> r2 2 4
> > x$c1
> NULL
> > x$c2
> NULL
>
Is this useful?--
> x[,"c1"]
r1 r2
1 2
I have only seen "$" used with lists. A data frame is a kind
of list, but a matrix isn't.
>From the R Reference Manual: "The form [of indexing] using $
applies to recursive objects such as lists and pairlists."
HTH
Mike Prager
Southeast Fisheries Science Center, NOAA
Beaufort, North Carolina USA
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