[Rd] access an element with empty name

[Kurt Hornik]

>>>>> Serguei Sokol writes:

> Hi,
> I came across a case where I cannot access a list element by its empty name.
> Minimal example can be constructed as

>      x=list("A", 1)
>      names(x)=c("a", "")
>      x[["a"]]
>      #[1]  "A"
>      x[[""]]
>      #NULL
>      x$`a`
>      #[1]  "A"
>      x$``
>      # Error: attempt to use zero-length variable name
>      # but we can still access the second element by its index
>      x[[2]]
>      #[1] 1

> To my mind, it should be perfectly legal to access an element by an 
> empty name as we can have for example
>      match("", names(x))
>      #[1] 2
> Hence a traditional question: is it a bug or feature?

A feature according to the docs: ? Extract says

    Neither empty (‘""’) nor ‘NA’ indices match any names, not even
    empty nor missing names. 

-k



> Best,
> Serguei.


>> sessionInfo()
> R version 3.5.0 (2018-04-23)
> Platform: x86_64-pc-linux-gnu (64-bit)
> Running under: Mageia 6

> Matrix products: default
> BLAS/LAPACK: /home/opt/OpenBLAS/lib/libopenblas_sandybridge-r0.3.0.dev.so

> locale:
> [1] C

> attached base packages:
> [1] stats     graphics  grDevices utils     datasets  methods base

> loaded via a namespace (and not attached):
> [1] compiler_3.5.0

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