[Rd] Quiz: How to get a "named column" from a data frame
Joshua Ulrich
josh.m.ulrich at gmail.com
Sat Aug 18 17:16:09 CEST 2012
I don't know if this is better, but it's the most obvious/shortest I
could come up with. Transpose the data.frame column to a 'row' vector
and drop the dimensions.
R> identical(nv, drop(t(df)))
[1] TRUE
Best,
--
Joshua Ulrich | about.me/joshuaulrich
FOSS Trading | www.fosstrading.com
On Sat, Aug 18, 2012 at 10:03 AM, Martin Maechler
<maechler at stat.math.ethz.ch> wrote:
> Today, I was looking for an elegant (and efficient) way
> to get a named (atomic) vector by selecting one column of a data frame.
> Of course, the vector names must be the rownames of the data frame.
>
> Ok, here is the quiz, I know one quite "cute"/"slick" answer, but was
> wondering if there are obvious better ones, and
> also if this should not become more idiomatic (hence "R-devel"):
>
> Consider this toy example, where the dataframe already has only
> one column :
>
>> nv <- c(a=1, d=17, e=101); nv
> a d e
> 1 17 101
>
>> df <- as.data.frame(cbind(VAR = nv)); df
> VAR
> a 1
> d 17
> e 101
>
> Now how, can I get 'nv' back from 'df' ? I.e., how to get
>
>> identical(nv, .......)
> [1] TRUE
>
> where ...... only uses 'df' (and no non-standard R packages)?
>
> As said, I know a simple solution (*), but I'm sure it is not
> obvious to most R users and probably not even to the majority of
> R-devel readers... OTOH, people like Bill Dunlap will not take
> long to provide it or a better one.
>
> (*) In my solution, the above '.......' consists of 17 letters.
> I'll post it later today (CEST time) ... or confirm
> that someone else has done so.
>
> Martin
>
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