Hi there,
I'm new working with R and I am trying to find the unchosen set of islands
that are closer to all the possible combination (of 2 out of 13) of a set of
chosen islands.
In other words, if I have a set of 13 islands (1, 2, ...13) and choose all
the possible combination of 2 islands (1-2, 1-3,...12-13) for each chosen
pair of islands which of the unchosen islands are the closest.

My code is below, but the problem is the loops seem not to be  working

library(gtools)
library(session

n=length(a)


closeout=matrix(NA,nrow=78, ncol=2)

for (i in 2){
x<-combinations(13,i) #considering these i islands

others=matrix(nrow=78, ncol=2)
for (j in 1:78){ #for all combinations of i islands
acopy=a #make a copy of a for manipulation
a<-as.matrix(a)

#finding out which islands are selected and removing them from consideration
others=paste('(acopy==',x[j,1],sep='')

for(islands in 1:2){
others=paste(others,' |acopy==',x[j,islands],sep='')
others=paste(others,')',sep='')
}
acopy[eval(parse(text=others))]=NA

#loop through each island in this set of islands and get closest island, but
exclude islands already counted
for(k in 1:i){
closeout[i,1]=a[x[j,],is.finite(as.numeric(a[x[j,k],]))][1]
closeout[i,2]=a[x[j,k],is.finite(as.numeric(a[x[j,k],]))][1]

acopy[a==closeout[i,]]=NA
}
}
write.csv(closeout, paste('res_closest',i,sep='','.csv'))

}

#################
The data of which island is closer to which is:
a
 V1 V2 V3 V4 V5 V6 V7 V8 V9 V10 V11 V12
 [1,]  8  2  4  9 13  3 11 12 10   5   6   7
 [2,]  1  8  4  9 13  3 11 12 10   5   6   7
 [3,] 13 11  9 12  5 10  4  6  7   8   1   2
 [4,]  9  8 13  3 11  1 12 10  5   2   6   7
 [5,] 12  6  3 10 11  7 13  9  4   8   1   2
 [6,]  7 10  5 12 11  3 13  9  4   8   1   2
 [7,]  6 10  5 12 11  3 13  9  4   8   1   2
 [8,]  1  4  2  9 13  3 11 12 10   5   6   7
 [9,] 13  3  4 11 12 10  5  8  6   1   7   2
[10,] 12 11 13  6  5  3  7  9  4   8   1   2
[11,] 13 12 10  3  9  5  6  4  7   8   1   2
[12,] 10 11 13  3  5  6  9  7  4   8   1   2
[13,]  9 11  3 12 10  4  5  6  7   8   1   2

Each row is an island and column V1 is the closest island to the islands, V2
the 2nd closest island....V12 is the farthest island.

Any help provided would be greatly appreciated,

Rocio





-- 
Rocio Ponce-Reyes
PhD Candidate
The Ecology Center
University of Queensland
St. Lucia QLD 4072

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