[R] $ subset operator behavior in lapply

[Hilmar Berger]

Hi Andrew,

thanks a lot, that fully explains it.

Sorry for the HTML text. For the record I put the original code again
below.

Best regards

Hilmar


On 27.10.22 18:34, Andrew Simmons wrote:
> $ does not evaluate its second argument, it does something like
> as.character(substitute(name)).
>
> You should be using
>
> lapply(list, function(x) x$a)
>
> or
>
> lapply(list, `[[`, "a")
>
>
> On Thu, Oct 27, 2022, 12:29 Hilmar Berger <hilmar.berger using gmx.de> wrote:
>
>     Dear all,
>
>     I'm a little bit surprised by the behavior of the $ operator when used
>     in lapply - any indication what might be wrong is appreciated.
>

 > xx = list(A=list(a=1:3, b=LETTERS[1:3]),"B"=list(a=7:9, b=LETTERS[7:9]))
 > lapply(xx,`$`,"a")
$A
NULL

$B
NULL

 > `$`(xx[[1]],"a")
[1] 1 2 3
 > lapply(xx,`[`,"a")
$A
$A$a
[1] 1 2 3


$B
$B$a
[1] 7 8 9


>     Any idea why I
>     `$`(object, name) works when applied to the single list element
>     but not
>     within lapply (in contrast to `[`)?
>     I checked the help page of the extraction operators but could not find
>     anything that explains this. Thanks and best regards Hilmar >
>     sessionInfo() R version 4.2.1 (2022-06-23) Platform:
>     x86_64-pc-linux-gnu
>     (64-bit) Running under: Ubuntu 20.04.5 LTS Matrix products: default
>     BLAS: /usr/lib/x86_64-linux-gnu/openblas-pthread/libblas.so.3 LAPACK:
>     /usr/lib/x86_64-linux-gnu/openblas-pthread/liblapack.so.3 locale: [1]
>     LC_CTYPE=en_US.UTF-8 LC_NUMERIC=C [3] LC_TIME=de_DE.UTF-8
>     LC_COLLATE=en_US.UTF-8 [5] LC_MONETARY=de_DE.UTF-8
>     LC_MESSAGES=en_US.UTF-8 [7] LC_PAPER=de_DE.UTF-8 LC_NAME=C [9]
>     LC_ADDRESS=C LC_TELEPHONE=C [11] LC_MEASUREMENT=de_DE.UTF-8
>     LC_IDENTIFICATION=C attached base packages: [1] stats graphics
>     grDevices
>     utils datasets methods base loaded via a namespace (and not attached):
>     [1] compiler_4.2.1
>
>             [[alternative HTML version deleted]]
>
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