[R] Create pairwise table from columns?

[Bill.Venables at csiro.au]

Here is a suggestion

> con <- textConnection("AnimalA,AnimalB,Score
    A1,A2,1
    A1,A3,2
    A1,A4,3
    A2,A3,4
    A2,A4,5
    A3,A4,6
    ")
> tst <- read.csv(con)
> close(con)
> an <- with(tst, sort(unique(c(as.character(AnimalA),
                    as.character(AnimalB)))))
> M <- array(0, c(length(an), length(an)), list(an, an))
> i <- match(tst$AnimalA, an)
> j <- match(tst$AnimalB, an)
> M[cbind(i,j)] <- M[cbind(j,i)] <- tst$Score
> 
> M
   A1 A2 A3 A4
A1  0  1  2  3
A2  1  0  4  5
A3  2  4  0  6
A4  3  5  6  0
> 


Bill Venables
CSIRO Laboratories
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http://www.cmis.csiro.au/bill.venables/ 

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
On Behalf Of knussear
Sent: Saturday, 10 May 2008 10:18 AM
To: r-help at r-project.org
Subject: [R] Create pairwise table from columns?


Hi Group

I have a large data set of individual pairwise values (250,000 rows)
that I
need to reshape into a pairwise matrix for mantel tests of these values
versus genetic distances.

the data are currently in columns formatted like so
AnimalA, AnimalB, Score
A1, A2, S1
A1, A3, S2
A1, A4, S3
A2, A3, S4
A2, A4, S5
A3, A4, S6
...,....,....


I need the final matrix to be formatted as
     A1    A2    A3    A4
A1  0     S1    S2    S3
A2  S1    0     S4    S5
A3  S2    S4   0      S6
A4  S3    S4   S6     0

are there any functions/packages that will make this easier?

Thanks

Ken
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