[Rd] Quiz: How to get a "named column" from a data frame
gunter.berton at gene.com
Sat Aug 18 18:37:19 CEST 2012
Yes, but either
does work. My minimal effort to check timings found that the first
version was a hair faster.
On Sat, Aug 18, 2012 at 9:01 AM, Rui Barradas <ruipbarradas at sapo.pt> wrote:
> A bit more general
> nv <- c(a=1, d=17, e=101); nv
> nv2 <- c(a="a", d="d", e="e")
> df2 <- data.frame(VAR = nv, CHAR = nv2); df2
> identical( nv, drop(t( df2 )) ) # TRUE
> identical( nv, drop(t( df2[] )) ) # FALSE
> Rui Barradas
> Em 18-08-2012 16:16, Joshua Ulrich escreveu:
>> 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)))
>>  TRUE
>> 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
>>> a 1
>>> d 17
>>> e 101
>>> Now how, can I get 'nv' back from 'df' ? I.e., how to get
>>>> identical(nv, .......)
>>>  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.
>>> R-devel at r-project.org mailing list
>> R-devel at r-project.org mailing list
> R-devel at r-project.org mailing list
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