Re: how to extract the elements of a list of vectors in a fixed position?

[David L Lorenz <lorenz@usgs.gov>]

Carol,
  If you know in advance that all
vectors have the same length, then you can convert the list to a data.frame
and extract the data in the row that you want. Try

as.data.frame(list (c(1,2), c(3, 4)))[2,]

returns
  X.1 X.2 
2   2   4

  Note that if the length of the
vectors are not all the same, as.data.frame will fail unless the length
of all of the shorter vectors are numeric factors of the length of the
longest vector so that the values are replicated correctly. Note that it
also names the components
  There is also a deprecated function
as.data.sheet(), which is in S-PLUS 7.0, that will allow you to convert
the list to a rectangular object so that you can extract any row you want.
It will return a value of NA for any vector shorter than the requested
element.
  There are good reasons for deprecating
the function, but there are times when it comes in handy like this.
Dave

carol white <wht_crl@yahoo.com>
Sent by: s-news-owner@lists.biostat.wustl.edu

11/15/2007 12:13 PM

To	s-news@lists.biostat.wustl.edu
cc
Subject	[S] how to extract the elements of a list of vectors in a fixed position?

Hi,
How is it possible to extract the elements of a list of vectors in a fixed
position? suppose that I have a list of 2-element vectors, how can I extract
the 2nd element of all vectors in the list? Can it be done with indexing
and not by element name because my elements don't have name?

Thanks 

carol

So in this example, I want to extract 2 and 4
v = list (c(1,2), c(3, 4))
 
> v
[[1]]
[1] 1 2

[[2]]
[1] 3 4

 

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