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

[Steve Martin]

Jiří,

For your first question, the NA names make sense if you think of indexing with a character vector as the same as menu[match(select, names(menu))]. You're not indexing with "beans"; rather, "beans" becomes NA because it's not in the names of menu. (This is how it's documented in ?`[`: "Character vectors will be matched to the names of the object...")

Steve


On Thursday, January 18th, 2024 at 2:51 PM, Jiří Moravec <jiri.c.moravec using gmail.com> 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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