From J.C.Rougier@durham.ac.uk  Tue Apr 24 09:49:16 2001
From: J.C.Rougier@durham.ac.uk (Jonathan Rougier)
Date: Tue, 24 Apr 2001 09:49:16 +0100 (BST)
Subject: [Rd] several bugs (PR#918) lists and matrices
In-Reply-To: <20010423141220.X25202@jimmy.harvard.edu>
Message-ID: <Pine.GSO.4.20.0104240935040.6372-100000@laplace>

Hi Robert,

On Mon, 23 Apr 2001, Robert Gentleman wrote:

>   I am uncertain as to why you want to put dimensions on a list? It
>   doesn't make it a matrix. That said we can duplicate the behaviour
>   but I'm not sure that it is worth introducing the confusion that
>   ought to follow.

Just to second Rich's reply: I love putting dimensions on a list!  I often
have rectangular data-structures of heterogeneous objects, and find it
much easier to operate with one large structure than several matching
small ones.

For example, at the moment I have a dynamic programming problem in which I
need to retain the expected payoff and the action, plus possibly some
other stuff as well, on a 2-grid.  I find it natural to write

dprog <- array(list(), c(20, 30))

# solving the dynamic programme

for (i in 20:1) for (j in 1:30) {

  # stuff here

  dprog[[i, j]] <- list(Ep = -1.0, action = "run for the hills")

  # and then, if I need to ...

  dprog[[i, j]]$andAnotherThing <- "don't look back"

}

Cheers, Jonathan.

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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[Rd] several bugs (PR#918) lists and matrices
Jonathan Rougier