Quiz: How to get a "named column" from a data frame
On Sat, Aug 18, 2012 at 5:14 PM, Christian Brechb?hler .... wrote:
On Sat, Aug 18, 2012 at 11:03 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)?
identical(nv, df[,1])
[1] TRUE
In my solution, the above '.......' consists of 17 letters.
I count 6 in mine
But it is not a solution in a current version of R! though it's still interesting that df[,1] worked in some incantation of R. What's your sessionInfo()? Martin
/Christian