Thank you, David. I missed the key detail.
Then Arun's option doesn't work as I need to parametrise needed columns
(they will be a vector).
Dimitri
On Tue, Feb 12, 2013 at 6:04 PM, David Winsemius <dwinsem...@comcast.net>wrote:
>
> On Feb 12, 2013, at 3:01 PM, Dimitri Liakhovitski wrote:
>
> > Arun, do you know why the first line works and the second doesn't?
> > newlist<-mapply(`[`,mylist,list(1,2,0),SIMPLIFY=FALSE) # it works
> > neededcolumns<-c(1,2,0) # it does not work
> > newlist<-mapply(`[`,mylist,list(neededcolumns),SIMPLIFY=FALSE)
>
> > list(c(1,2,3))
> [[1]]
> [1] 1 2 3
>
> > list(1,2,3)
> [[1]]
> [1] 1
>
> [[2]]
> [1] 2
>
> [[3]]
> [1] 3
>
>
> --
> David.
> > Dimitri
> > On Tue, Feb 12, 2013 at 5:08 PM, arun <smartpink...@yahoo.com> wrote:
> >
> >> Hi,
> >>
> >>
> >> mapply(`[`,mylist,list(1,2,0),SIMPLIFY=FALSE)
> >> #[[1]]
> >> # a
> >> #1 1
> >> #2 2
> >>
> >> #[[2]]
> >> # b
> >> #1 5
> >> #2 6
> >>
> >> #[[3]]
> >> #data frame with 0 columns and 2 rows
> >>
> >>
> >> A.K.
> >>
> >> ----- Original Message -----
> >> From: Dimitri Liakhovitski <dimitri.liakhovit...@gmail.com>
> >> To: r-help <r-help@r-project.org>
> >> Cc:
> >> Sent: Tuesday, February 12, 2013 4:33 PM
> >> Subject: [R] grabbing from elements of a list without a loop
> >>
> >> Hello!
> >>
> >> # I have a list with several data frames:
> >> mylist<-list(data.frame(a=1:2,b=2:3),
> >> data.frame(a=3:4,b=5:6),data.frame(a=7:8,b=9:10))
> >> (mylist)
> >>
> >> # I want to grab only one specific column from each list element
> >> neededcolumns<-c(1,2,0) # number of the column I need from each
> element of
> >> the list
> >>
> >> # Below, I am doing it using a loop:
> >> newlist<-NULL
> >> for(i in 1:length(mylist) ) {
> >> newlist[[i]]<-mylist[[i]] [neededcolumns[i]]
> >> }
> >> newlist<-do.call(cbind,newlist)
> >> (newlist)
> >>
> >> I was wondering if there is any way to avoid the loop above and make it
> >> faster.
> >> In reality, I have a much longer list, each of my data frames is much
> >> larger and I have to do it MANY-MANY times.
> >> Thanks a lot!
> >>
> >> Dimitri Liakhovitski
> >> gfk.com <http://marketfusionanalytics.com/>
> >>
> >> [[alternative HTML version deleted]]
> >>
> >> ______________________________________________
> >> R-help@r-project.org mailing list
> >> https://stat.ethz.ch/mailman/listinfo/r-help
> >> PLEASE do read the posting guide
> >> http://www.R-project.org/posting-guide.html<http://www.r-project.org/posting-guide.html>
> <http://www.r-project.org/posting-guide.html>
> >> and provide commented, minimal, self-contained, reproducible code.
> >>
> >>
> >
> >
> > --
> > Dimitri Liakhovitski
> > gfk.com <http://marketfusionanalytics.com/>
> >
> > [[alternative HTML version deleted]]
> >
> > ______________________________________________
> > R-help@r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-help
> > PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html<http://www.r-project.org/posting-guide.html>
> > and provide commented, minimal, self-contained, reproducible code.
>
> David Winsemius
> Alameda, CA, USA
>
>
--
Dimitri Liakhovitski
gfk.com <http://marketfusionanalytics.com/>
[[alternative HTML version deleted]]
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