Cool.
Using [[var]] instead of $var to extract the expected variable is really
what i want.
Thanks. Guys.
2010/4/7 Steve Lianoglou <mailinglist.honey...@gmail.com>
> Hi,
>
> On Wed, Apr 7, 2010 at 6:27 PM, rusers.sh <rusers...@gmail.com> wrote:
> > Hi all,
> > My problem may be related with the list manipulations. See below.
> > #example data
> > a<-list()
> > a[[1]]<-data.frame(matrix(c(1:4),ncol=2));
> > a[[2]]<-data.frame(matrix(c(5:8),ncol=2))
> > I can use a[[1]]$X1,a[[1]]$X2,a[[2]]$X1,a[[2]]$X2 to use the
> corresponding
> > variables. But what i need to do is to use function parameters to specify
> > the variable names. The variable names will be different for various
> > dataset, so i need a common place to indicate it.
> > Something like,
> > b<-function(var1=X1,var2=X2) {
> > for (n in 1:2) {
> > paste("a", "[[",n, "]]","$","var1", sep="")
> > paste("a", "[[",n, "]]","$","var2", sep="")
> > }
> > }
> > b(var1=X1,var2=X2) will have the same effect
> > as a[[1]]$X1,a[[1]]$X2,a[[2]]$X1,a[[2]]$X2. Unfortunately, it does not
> > work.
> > Anybody can give me some suggestions on this? Hope it is clear for this
> > question.
>
> I'm not really sure what you're trying to do, but if you just want to
> select out certain columns of a data.frame by passing the name of the
> column around in someway, pass its name as a string and select the
> collumn using [[var]] instead of $var.
>
> For instance, using your data.frame ``a``. Say I want to either pull
> out 'X1', or 'X2', you could do:
>
> R> some.column <- 'X1'
> R> a[[1]][[some.column]]
>
> So whatever you are trying to do in your b() function, maybe you would
> change it like so:
>
> b <- function(var1='X1', var2='X2') {
> ## notice 'X1' and 'X2' are in quote in mine
> ...
> cat(a[[n]][[var1]], '\n')
> }
>
> Also -- your call to `paste` isn't doing what I think you think it's
> doing (what do you want it to do?)
>
> Does that get you closer to what you need?
>
> -steve
>
> --
> Steve Lianoglou
> Graduate Student: Computational Systems Biology
> | Memorial Sloan-Kettering Cancer Center
> | Weill Medical College of Cornell University
> Contact Info: http://cbio.mskcc.org/~lianos/contact
>
--
-----------------
Jane Chang
Queen's
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