Re: [R] "[[" gotcha

From: Petr Pikal <petr.pikal_at_precheza.cz>
Date: Tue 16 Jan 2007 - 10:43:03 GMT


Hi

try different way of list definition, see below.

On 16 Jan 2007 at 10:10, Robin Hankin wrote:

From:           	Robin Hankin <r.hankin@noc.soton.ac.uk>
Date sent:      	Tue, 16 Jan 2007 10:10:42 +0000
To:             	RHelp help <r-help@stat.math.ethz.ch>
Subject:        	[R] "[[" gotcha

> The following gotcha caught me off-guard just now.
>
> I have two matrices, a and b:
>
>
> a <- matrix(1,3,3)
> b <- matrix(1,1,1)
>
> (note that both "a" and "b" are matrices).
>
> I want them in a list:
>

B<-vector("list", 2)
B[[1]]<-a
B[[1]]<-b

here is no complain.
HTH
Petr

> > B <- NULL
> > B[[1]] <- a
> > B[[2]] <- b
> > B
> [[1]]
> [,1] [,2] [,3]
> [1,] 1 1 1
> [2,] 1 1 1
> [3,] 1 1 1
>
> [[2]]
> [,1]
> [1,] 1
>
> >
>
> This is fine.
>
> But swapping "a" and "b" over does not behave as desired:
>
>
> > B <- NULL
> > B[[1]] <- b
> > B[[2]] <- a
> Error in B[[2]] <- a : more elements supplied than there are to
> replace
> >
>
>
>
> The error is given because after B[[1]] <- a, the variable B is
> just a scalar and not a matrix (why is this?)
>
> What's the bulletproof method for assigning matrices to a list (whose
> length is not known at runtime)?
>
>
>
>
>
>
>
>
> --
> Robin Hankin
> Uncertainty Analyst
> National Oceanography Centre, Southampton
> European Way, Southampton SO14 3ZH, UK
> tel 023-8059-7743
>
> ______________________________________________
> R-help@stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html and provide commented,
> minimal, self-contained, reproducible code.

Petr Pikal
petr.pikal@precheza.cz



R-help@stat.math.ethz.ch mailing list
https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. Received on Tue Jan 16 22:13:45 2007

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