From: Martin Maechler <maechler_at_stat.math.ethz.ch>

Date: Sat, 18 Aug 2012 18:33:36 +0200

* >> 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 :
*

* >>
*

>> a d e

* >> 1 17 101
*

* >>
*

* >> VAR
*

>> a 1

* >> d 17
*

* >> e 101
*

* >>
*

* >> Now how, can I get 'nv' back from 'df' ? I.e., how to get
*

* >>
*

** >> [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
*

R-devel_at_r-project.org mailing list

https://stat.ethz.ch/mailman/listinfo/r-devel Received on Sat 18 Aug 2012 - 17:12:47 GMT

Date: Sat, 18 Aug 2012 18:33:36 +0200

>>>>> Joshua Ulrich <josh.m.ulrich_at_gmail.com> >>>>> on Sat, 18 Aug 2012 10:16:09 -0500 writes:

> 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
**
Yes, that's definitely shorter,

congratulations!

One gotta is that I'd want a solution that also works when the df has more columns than just one...

Your idea to use t(.) is nice and "perfect" insofar as it coerces the data frame to a matrix, and that's really the clue:

Where as df[,1] is losing the names,
the matrix indexing is not.

So your solution can be changed into

t(df)[1,]

as.matrix(df)[,1]

Now, the remaining question is: Shouldn't there be something
more natural to achieve that?

(There is not, currently, AFAIK).

Martin

> 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:

>> (atomic) vector by selecting one column of a data frame. Of course,

>>> nv <- c(a=1, d=17, e=101); nv

>> a d e

>>> df <- as.data.frame(cbind(VAR = nv)); df

>>> identical(nv, .......)

R-devel_at_r-project.org mailing list

https://stat.ethz.ch/mailman/listinfo/r-devel Received on Sat 18 Aug 2012 - 17:12:47 GMT

This quarter's messages: by month, or sorted: [ by date ] [ by thread ] [ by subject ] [ by author ]

*
Archive maintained by Robert King, hosted by
the discipline of
statistics at the
University of Newcastle,
Australia.
Archive generated by hypermail 2.2.0, at Wed 22 Aug 2012 - 14:30:40 GMT.
*

*
Mailing list information is available at https://stat.ethz.ch/mailman/listinfo/r-devel.
Please read the posting
guide before posting to the list.
*