From josh.m.ulrich at gmail.com  Sat Aug 18 17:16:09 2012
From: josh.m.ulrich at gmail.com (Joshua Ulrich)
Date: Sat, 18 Aug 2012 10:16:09 -0500
Subject: [Rd] Quiz: How to get a "named column" from a data frame
In-Reply-To: <20527.44736.486888.854733@stat.math.ethz.ch>
References: <20527.44736.486888.854733@stat.math.ethz.ch>
Message-ID: <CAPPM_gRmc+VE3ZGJ3TzTn6m4qb4ToUq30X0USATmmEjxq3u4dA@mail.gmail.com>

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



[Rd] Quiz: How to get a "named column" from a data frame
Joshua Ulrich