From ggrothendieck at gmail.com  Sat Nov 29 12:31:11 2008
From: ggrothendieck at gmail.com (Gabor Grothendieck)
Date: Sat, 29 Nov 2008 06:31:11 -0500
Subject: [Rd] names generated in list indexing
In-Reply-To: <22D850BC39A25742977325ADDE208E770270618DAB@chiexchange02.w2k.jumptrading.com>
References: <22D850BC39A25742977325ADDE208E770270618DAB@chiexchange02.w2k.jumptrading.com>
Message-ID: <971536df0811290331v7e02351ayc02ef90f29ebc866@mail.gmail.com>

Also note the behavior is the same for a non-list vector:

> c(b=1)[c('a','b')]
<NA>    b
  NA    1

but differs for a data frame:

> data.frame(b=1)[c('a','b')]
Error in `[.data.frame`(data.frame(b = 1), c("a", "b")) :
  undefined columns selected


On Fri, Nov 28, 2008 at 2:03 PM, Vadim Ogranovich
<vogranovich at jumptrading.com> wrote:
> Dear R-devel,
>
> When a character vector is used to subscript a list and when some of the subscripts are not present in the list names R  returns NULL for those subscripts and generate NA names for each of them:
>
>> list(b=1)[c('a','b')]
> $<NA>  <<-- generated name
> NULL
> $b
> [1] 1
>
>
> Wouldn't it be more intuitive to use the subscript name rather than to generate an NA? Something like this (not real result):
>> list(b=1)[c('a','b')]
> $a        <<-- more intuitive name
> NULL
> $b
> [1] 1
>
>
>> version
>               _
> platform       i386-pc-mingw32
> arch           i386
> os             mingw32
> system         i386, mingw32
> status
> major          2
> minor          7.1
> year           2008
> month          06
> day            23
> svn rev        45970
> language       R
> version.string R version 2.7.1 (2008-06-23)
>>
>
>
> Thanks,
> Vadim
>
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[Rd] names generated in list indexing
Gabor Grothendieck