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