Hi Dimitri,
neededcolumns<- c(1,2,0)
mapply(`[`,mylist,lapply(neededcolumns,function(x) x),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.
________________________________
From: Dimitri Liakhovitski <dimitri.liakhovit...@gmail.com>
To: arun <smartpink...@yahoo.com>
Cc: R help <r-help@r-project.org>
Sent: Tuesday, February 12, 2013 6:01 PM
Subject: Re: [R] grabbing from elements of a list without a loop
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)
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
>and provide commented, minimal, self-contained, reproducible code.
>
>
--
Dimitri Liakhovitski
gfk.com
______________________________________________
R-help@r-project.org mailing list
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
