[R] how to use list index to get vector
Gabor Grothendieck
ggrothendieck at gmail.com
Tue May 17 03:28:01 CEST 2005
Its the indexing function written in ordinary function form. That is,
foo[1:2] can be written as "["(foo, 1:2)
On 5/16/05, Luke <jyzz88 at gmail.com> wrote:
> Yes, it works. Althought I can understand the help page of sapply, I
> don't know why it works. What is "["?
>
> -Luke
>
> On 5/16/05, Gabor Grothendieck <ggrothendieck at gmail.com> wrote:
> > On 5/16/05, Luke <jyzz88 at gmail.com> wrote:
> > > I have a simple question, but I couldn't find the answer in R manuals.
> > >
> > > Assume I have a list:
> > > > foo <- list()
> > > > foo[[1]] <- c(1, 2, 3)
> > > > foo[[2]] <- c(11,22,33)
> > > > foo[[3]] <- c(111,222,333)
> > > > foo
> > > [[1]]
> > > [1] 1 2 3
> > >
> > > [[2]]
> > > [1] 11 22 33
> > >
> > > [[3]]
> > > [1] 111 222 333
> > >
> > > How to use list index to get a vector of, say, the first elements of
> > > list elements?
> > > That is, how to get a vector c(1, 11, 111) from foo?
> > >
> > > foo[[]][1] doesn't work.
> > >
> >
> > Try this:
> >
> > sapply(foo, "[", 1)
> >
>
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