[R] changing the form of a list

[Peter Dalgaard BSA]

"jimi adams" <imij at columbus.rr.com> writes:

> i have a 2 x n matrix that is a paired list of connections, i am working
> with that looks something like:
> 1 2
> 1 3
> 1 5
> 2 1
> 2 3
> 3 1
> 3 2
> 4 5
> 5 1
> 5 4
> for later operations it would be helpful if i could change this into the
> form of:
> 1  2 3 5
> 2  1 3
> 3  1 2
> 4  5
> 5  1 4

Something like this?

> zz <- matrix(scan(),ncol=2,byrow=T)
1: 1 2
3: 1 3
5: 1 5
7: 2 1
9: 2 3
11: 3 1
13: 3 2
15: 4 5
17: 5 1
19: 5 4
21: Read 20 items
> x <- zz[,1]
> y <- zz[,2]
> tapply(y,x,sort)
$"1"
[1] 2 3 5

$"2"
[1] 1 3

$"3"
[1] 1 2

$"4"
[1] 5

$"5"
[1] 1 4

You might want something slightly more complicated like

tapply(y,factor(x,levels=1:5), function(z) sort(unique(x))) 

to account for empty groups and duplicated pairs.

-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)             FAX: (+45) 35327907
-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
Send "info", "help", or "[un]subscribe"
(in the "body", not the subject !)  To: r-help-request at stat.math.ethz.ch
_._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._