replicating lists

hi,

Yes, I agree that the work-around needs some care, but I'm not sure
we need to wrap the list itself -- we're simply using properties of
"[" on lists.  If the subscript is rep(1, 10), then we'll get the
first element 10 times (which is *not* replicating the list).
To get the replication we need to index every element in
the list as many times as required.

David

Date: Wed, 11 Apr 2001 15:28:02 +0100 (BST)
From: Jonathan Rougier <J.C.Rougier@durham.ac.uk>
X-Sender: dma0jcr@laplace
To: David James <dj@research.bell-labs.com>
cc: r-devel@stat.math.ethz.ch
Subject: Re: [Rd] replicating lists
MIME-Version: 1.0

On Wed, 11 Apr 2001, David James wrote:

A workaround is to use rep() inside "[":

a <- list(a=1, b=2, c=3)
a[rep(1:3, 1:3)]

$a
[1] 1

$b
[1] 2

$b
[1] 2

$c
[1] 3

$c
[1] 3

$c
[1] 3

Note, however, that names are no longer unique!

This work-around is cunning but needs a bit of care, as to get the
replication of the whole of fred you need to wrap the list itself:

fred <- list(happy = 1:10, fred = "squash")
list(fred)[rep(1, 10)] # list with 10 copies of fred

Cheers, Jonathn.

Jonathan Rougier                       Science Laboratories
Department of Mathematical Sciences    South Road
University of Durham                   Durham DH1 3LE
tel: +44 (0)191 374 2361, fax: +44 (0)191 374 7388
http://www.maths.dur.ac.uk/stats/people/jcr/jcr.html

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