[R] [External] Dimensioning lists.

[Richard M. Heiberger]

Use double [[ ]]

> xxx[[2,3]]
$a
[1] "n"

$b
[1] 20

>

________________________________________
From: R-help <r-help-bounces using r-project.org> on behalf of Rolf Turner <r.turner using auckland.ac.nz>
Sent: Sunday, February 14, 2021 10:35 PM
To: "r-help using R-project.org\"  <r-help using R-project.org>"@r-project.org
Subject: [External] [R] Dimensioning  lists.


I have a setting in which it would be convenient to treat a list
as an array, i.e. to address its entries via a pair of indices.

A toy example:

xxx <- vector("list",9)
set.seed(42)
for(i in 1:9) xxx[[i]] <- list(a=sample(letters,1),b=sample(1:100,1))

I would like to be able to treat "xxx" as a 3 x 3 matrix.

I tried

   dim(xxx) <- c(3,3)

When I do, e.g.

    xxx[2,3]

I get:

> [[1]]
> [[1]]$a
> [1] "n"
>
> [[1]]$b
> [1] 20

That is I get a list of length 1, whose (sole) entry is the desired
object.  I would *like* to get just the desired object, *not* wrapped in
a list, i.e.:

> $a
> [1] "n"
>
> $b
> [1] 20
>

(which is what I get by typing xxx[2,3][[1]]).

Is there any way to prevent the entries of xxx from being wrapped up in
lists of length 1?

Thanks for any enlightenment.

cheers,

Rolf Turner

--
Honorary Research Fellow
Department of Statistics
University of Auckland
Phone: +64-9-373-7599 ext. 88276

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