[Rd] Should subsetting named vector return named vector including named unmatched elements?

[Hervé Pagès]

Never been a big fan of this behavior either but maybe the intention was 
to make it easier to distinguish between 2 types of NAs in the result: 
those that were present in the original vector vs those that are 
introduced by an unmatched subscript. Like in this example:

     x <- setNames(c(101:108, NA), letters[1:9])
     x
     #   a   b   c   d   e   f   g   h   i
     # 101 102 103 104 105 106 107 108  NA

     x[c("g", "k", "a", "i")]
     #    g <NA>    a    i
     #  107   NA  101   NA

The first NA is the result of an unmatched subscript, while the second 
one comes from 'x'.

This is of limited interest though. In most real world applications I've 
worked on, we actually need to "fix" the names of the result.

Best,

H.

On 1/18/24 11:51, Jiří Moravec wrote:
> Subsetting vector (including lists) returns the same number of 
> elements as the subsetting vector, including unmatched elements which 
> are reported as `NA` or `NULL` (in case of lists).
>
> Consider:
>
> ```
> menu = list(
>   "bacon" = "foo",
>   "eggs" = "bar",
>   "beans" = "baz"
>   )
>
> select = c("bacon", "eggs", "spam")
>
> menu[select]
> # $bacon
> # [1] "foo"
> #
> # $eggs
> # [1] "bar"
> #
> # $<NA>
> # NULL
>
> ```
>
> Wouldn't it be more logical to return named vector/list including 
> names of unmatched elements when subsetting using names? After all, 
> the unmatched elements are already returned. I.e., the output would 
> look like this:
>
> ```
>
> menu[select]
> # $bacon
> # [1] "foo"
> #
> # $eggs
> # [1] "bar"
> #
> # $spam
> # NULL
>
> ```
>
> The simple fix `menu[select] |> setNames(select)` solves, but it feels 
> to me like something that could be a default behaviour.
>
> On slightly unrelated note, when I was asking if there is a better 
> solution, the `menu[select]` seems to allocate more memory than 
> `menu_env = list2env(menu); mget(select, envir = menu, ifnotfound = 
> list(NULL)`. Or the sapply solution. Is this a benchmarking artifact?
>
> https://stackoverflow.com/q/77828678/4868692
>
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-- 
Hervé Pagès

Bioconductor Core Team
hpages.on.github using gmail.com

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