RE: [R] how to use list index to get vector

From: Liaw, Andy <andy_liaw_at_merck.com>
Date: Tue 17 May 2005 - 11:55:00 EST


If you have the data in files in such format, with one entry per line, you can do something like:

dat <- matrix(scan("fileWithData", sep=":"), ncol=2, byrow=TRUE)

Then the first column of dat would be the indices, and the second column would be the values.

Andy

> From: Luke
>
> Hi Gabor, thanks a lot. I understand it now. But Andrew's method is
> easier for me to understand. Can I extend my question? I have a data
> file, every line has such format:
> 2:102 5:85 ...
> The number before colon is data entry index, the number after colon is
> data entry value, and other data entries are zero. I use scan to read
> them in R and need to separate the index and value to different
> vectors. For example:
>
> > foo
> [1] "2:102" "5:85"
> > foo2 <- strsplit(foo, split=":")
> > foo2
> [[1]]
> [1] "2" "102"
>
> [[2]]
> [1] "5" "85"
>
> > myIndex <- as.numeric(unlist(lapply(foo2, function(x) x[1])))
> or
> > myIndex <- as.numeric(foo2, "[", 1)
> > myIndex
> [1] "2" "5"
>
> Is this the simplest way to get the index or value vector?
>
> -Luke
>
> On 5/16/05, Gabor Grothendieck <ggrothendieck@gmail.com> wrote:
> > 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@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@gmail.com> wrote:
> > > > On 5/16/05, Luke <jyzz88@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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>



R-help@stat.math.ethz.ch mailing list
https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Tue May 17 11:58:40 2005

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