[R] getting all pairwise combinations of elements in a characterstring

Wills, Kellie Kellie.Wills at montgomerycollege.edu
Thu Feb 12 18:40:53 CET 2009


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

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