On Mar 26, 2011, at 9:44 AM, Brian Pellerin wrote:
Hello,
I would like to take advantage of the upper.tri() function here but
I don't
know exactly. Here is some working code...
i<-5
fi<-matrix(0,nrow=i,ncol=i)
for(r in 1:i){
for(c in 1:i){
if(r==c){
fi[r,c]<-1
}else if(r<c){
fi[r,c]<-1-runif(1)^.5
}else{
fi[r,c]<-fi[c,r]
}
}
}
So far I know I can simplify this code to 5 lines (no for loops):
i<-5
fi<-matrix(nrow=i,ncol=i)
fi[upper.tri(fi)]<-1-runif(length(fi[upper.tri(fi)]))^.5
diag(fi)<-1
fi[lower.tri(fi)]<-fi[upper.tri(fi)]#This entry is not correct.
fi[r,c] ! ==
fi[c,r]
I've always found using the upper.tri and lower.tri functions error
prone in my hands, because they are really logical matrices for
selection rather than returning values as I naively expect. Try this:
i<-5
fi<-diag(1,i,i)
fi[upper.tri(fi)]<-1-runif(length(fi[upper.tri(fi)]))^.5
fi[lower.tri(fi)]<-t(fi)[lower.tri(fi)]
fi
It may seem odd to use lower.tri(fi) inside `[ ]` since the values of
`fi` in the lower triangle are all zero, but you are really just using
it to extract from `t(fi)`.
--
David.
Any suggestions?
Sincerely,
Brian
[[alternative HTML version deleted]]
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David Winsemius, MD
West Hartford, CT
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and provide commented, minimal, self-contained, reproducible code.
