From Kurt@Hornik @ending from wu@@c@@t  Mon May 14 15:55:47 2018
From: Kurt@Hornik @ending from wu@@c@@t (Kurt Hornik)
Date: Mon, 14 May 2018 15:55:47 +0200
Subject: [Rd] access an element with empty name
In-Reply-To: <0477dba5-4e80-84ab-7ea5-51b670de88fc@insa-toulouse.fr>
References: <0477dba5-4e80-84ab-7ea5-51b670de88fc@insa-toulouse.fr>
Message-ID: <23289.38243.173216.323929@hornik.net>

>>>>> 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

> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel



[Rd] access an element with empty name
Kurt Hornik