R help - Feb 2009 - getting all pairwise combinations of elements in a character string

I'm able to do this as follows, but am wondering if anyone knows a 
simpler way which still avoids explicit loops?

 > (mystring <- letters[1:5])
[1] "a" "b" "c" "d" "e"
 > unlist(sapply(mystring[-length(mystring)],
+               function(x) 
paste(x,mystring[(grep(x,mystring)+1):length(mystring)],sep="")))
  a1   a2   a3   a4   b1   b2   b3   c1   c2    d
"ab" "ac" "ad" "ae" "bc"
"bd" "be" "cd" "ce" "de"
 >


-- 
Levi Waldron
post-doctoral fellow
Jurisica Lab, Ontario Cancer Institute
Division of Signaling Biology
IBM Life Sciences Discovery Centre
TMDT 9-304D
101 College Street
Toronto, Ontario M5G 1L7

How about

m <- outer(mystring, mystring, paste, sep="")
m[upper.tri(m)]

Kellie Wills


-----Original Message-----
From: r-help-bounces at r-project.org on behalf of Levi Waldron
Sent: Thu 2/12/2009 12:20 PM
To: r-help at r-project.org
Subject: [R] getting all pairwise combinations of elements in a characterstring
 
I'm able to do this as follows, but am wondering if anyone knows a 
simpler way which still avoids explicit loops?

 > (mystring <- letters[1:5])
[1] "a" "b" "c" "d" "e"
 > unlist(sapply(mystring[-length(mystring)],
+               function(x) 
paste(x,mystring[(grep(x,mystring)+1):length(mystring)],sep="")))
  a1   a2   a3   a4   b1   b2   b3   c1   c2    d
"ab" "ac" "ad" "ae" "bc"
"bd" "be" "cd" "ce" "de"
 >


-- 
Levi Waldron
post-doctoral fellow
Jurisica Lab, Ontario Cancer Institute
Division of Signaling Biology
IBM Life Sciences Discovery Centre
TMDT 9-304D
101 College Street
Toronto, Ontario M5G 1L7

______________________________________________
R-help at r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.

> combn(letters[1:5], 2)
     [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
[1,] "a"  "a"  "a"  "a"  "b" 
"b"  "b"  "c"  "c"  "d"
[2,] "b"  "c"  "d"  "e"  "c" 
"d"  "e"  "d"  "e" 
"e"
>

On Thu, Feb 12, 2009 at 12:20 PM, Levi Waldron
<lwaldron at uhnres.utoronto.ca> wrote:
> I'm able to do this as follows, but am wondering if anyone knows a
simpler
> way which still avoids explicit loops?
>
>> (mystring <- letters[1:5])
> [1] "a" "b" "c" "d" "e"
>> unlist(sapply(mystring[-length(mystring)],
> +               function(x)
> paste(x,mystring[(grep(x,mystring)+1):length(mystring)],sep="")))
>  a1   a2   a3   a4   b1   b2   b3   c1   c2    d
> "ab" "ac" "ad" "ae" "bc"
"bd" "be" "cd" "ce" "de"
>>
>
>
> --
> Levi Waldron
> post-doctoral fellow
> Jurisica Lab, Ontario Cancer Institute
> Division of Signaling Biology
> IBM Life Sciences Discovery Centre
> TMDT 9-304D
> 101 College Street
> Toronto, Ontario M5G 1L7
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>


-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390

What is the problem that you are trying to solve?

I like both of these solutions much better - thank you!
-Levi

-- 
Levi Waldron
post-doctoral fellow
Jurisica Lab, Ontario Cancer Institute
Division of Signaling Biology
IBM Life Sciences Discovery Centre
TMDT 9-304D
101 College Street
Toronto, Ontario M5G 1L7