R help - Nov 2008 - Manipulating lists

Hello R-Community,

I am pretty new to R and I am fascinated what R can do! I am doing 
phylogenetic analysis in R, and my current project includes two problems 
that I am unable to solve, unfortunately. I am hoping that someone knows 
an easy, and R-typical solution, any help would be appreciated. 
Specifically, I have the following two problems:

1) I am reading in all the files from a directory using file_list <- 
list.files(). It works, of course, however, I want to restrict file_list 
to files that end with ".nex". Thus, I want to remove some files from 
this list. I read that I can do something like file_list <- 
file_list[condition]. I do not know how to express my condition here, 
unfortunately. Pseudo code would be something like file_list <- 
file_list[ends with ".nex"]

2) A slightly more complicated problem, at least I think that. I have 
two lists, list1 and list2. list1 contains some elements (characters 
such as "species1"). list2 contains also species names, including all
of
list1, but also species that are not part of list1. I need a way to 
create a list that contains ONLY those elements that are in list2, but 
not in list1.
For example: list1 =
c("s1","s3","s4","s7"), list2 =
c("s1","s2","s3","s4","s5","s6","s7"),
now I need a way to create the
list list3 = c("s2","s5","s6"). Any ideas? I am
not able to find the
appropriate function...

Thanks
Christian

On Sun, Nov 16, 2008 at 9:56 PM, Christian Arnold <chrarnold at web.de>
wrote:
> Hello R-Community,
>
> I am pretty new to R and I am fascinated what R can do! I am doing
> phylogenetic analysis in R, and my current project includes two problems
> that I am unable to solve, unfortunately. I am hoping that someone knows an
> easy, and R-typical solution, any help would be appreciated. Specifically,
I
> have the following two problems:
>
> 1) I am reading in all the files from a directory using file_list <-
> list.files(). It works, of course, however, I want to restrict file_list to
> files that end with ".nex". Thus, I want to remove some files
from this
> list. I read that I can do something like file_list <-
file_list[condition].
> I do not know how to express my condition here, unfortunately. Pseudo code
> would be something like file_list <- file_list[ends with
".nex"]
Maybe you could use dir() instead - see particularly the pattern argument.
> 2) A slightly more complicated problem, at least I think that. I have two
> lists, list1 and list2. list1 contains some elements (characters such as
> "species1"). list2 contains also species names, including all of
list1, but
> also species that are not part of list1. I need a way to create a list that
> contains ONLY those elements that are in list2, but not in list1.
> For example: list1 =
c("s1","s3","s4","s7"), list2 >
c("s1","s2","s3","s4","s5","s6","s7"),
now I need a way to create the list
> list3 = c("s2","s5","s6"). Any ideas? I am
not able to find the appropriate
> function...
Have a look at setdiff.

Hadley


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