From: Winston Chang <winstonchang1_at_gmail.com>

Date: Sat, 18 Aug 2012 13:54:09 -0500

R-devel_at_r-project.org mailing list

https://stat.ethz.ch/mailman/listinfo/r-devel Received on Sat 18 Aug 2012 - 19:10:07 GMT

Date: Sat, 18 Aug 2012 13:54:09 -0500

This isn't super-concise, but has the virtue of being clear:

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

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

identical(nv, setNames(df$VAR, rownames(df)))
**# TRUE
**
It seems to be more efficient than the other methods as well:

f1 <- function() setNames(df$VAR, rownames(df)) f2 <- function() t(df)[1,] f3 <- function() as.matrix(df)[,1]

r <- microbenchmark(f1(), f2(), f3(), times=1000) r

# Unit: microseconds # expr min lq median uq max # 1 f1() 14.589 17.0315 18.608 19.3220 89.388 # 2 f2() 68.057 70.8735 72.240 75.8065 3707.012 # 3 f3() 58.153 61.2600 62.521 65.0380 238.483

-Winston

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
*

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