[Ooops. Forgot to copy the list 1st time around... Also missed the
possibility of using t()]
Robin Hankin <[EMAIL PROTECTED]> writes:
> Hi everyone.
>
> I'm playing with aperm():
>
> a <- 1:24
> dim(a) <- c(2,3,2,2)
> permutation <- c(1,2,4,3)
> b <- aperm(a,permutation)
>
>
> So if my understanding is right,
>
> a[1,3,2,1] == b[c(1,3,2,1)[permutation] ]
>
> but this isn't what I want because the RHS evaluates to a vector, and
> I am trying to identify a single element of b.
>
> How do I modify the RHS to give what I want?
Matrix indexing:
> a[1,3,2,1]
[1] 11
> b[rbind(c(1,3,2,1)[permutation])]
[1] 11
or, equivalently:
> b[matrix(c(1,3,2,1)[permutation],1)]
[1] 11
or (neat, once you get it)
> b[t(c(1,3,2,1)[permutation])]
[1] 11
> Following aren't right either:
> b[as.vector(c(1,3,2,1)[permutation]) ]
> b[as.list(c(1,3,2,1)[permutation]) ]
>
>
> OBattempt:
> eval(parse(text=paste("b[",paste(c(1,3,2,1)[permutation],collapse=","),"]")))
>
> which DOES work, but is ghastly!
Less ghastly (but only slightly so):
> do.call("[",c(list(b),as.list(c(1,3,2,1)[permutation])))
[1] 11
--
O__ ---- Peter Dalgaard Blegdamsvej 3
c/ /'_ --- Dept. of Biostatistics 2200 Cph. N
(*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918
~~~~~~~~~~ - ([EMAIL PROTECTED]) FAX: (+45) 35327907
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