On Apr 29, 2011, at 4:27 AM, ivan wrote:
Hi All,
I am trying to create a function which evaluates whether the values
(which
are equal to one) of a matrix are the same as their mirror values.
Consider
the following matrix:
n<-matrix(cbind(c(0,1,1),c(1,0,0),c(0,1,0)),3,3)
colnames(n)<-cbind("A","B","C");rownames(n)<-cbind("A","B","C")
n
A B C
A 0 1 0
B 1 0 1
C 1 0 0
Hence, since n[2,1] and n[1,2] are 1 and the same, the function should
return the name of the row of n[2,1]. I used the following function:
for (i in length(rownames(n))) {
for (j in length(colnames(n))){
if(n[i,j]==n[j,i]){
rownames(n)[[i]]->output} else {}
}
}
output
NULL
The right answer would have been "B", though.
Can you explain why "A" would not be an equally good answer to satisfy
your problem set up?
> which(n == t(n) & col(n) != row(n) , arr.ind=TRUE)
row col
B 2 1
A 1 2
> rownames(which(n == t(n) & col(n) != row(n) , arr.ind=TRUE) )
[1] "B" "A"
# Which would seem to be the correct answer, but
# This adds an additional constraint and also insures no diagonal
elements
> rownames(which(n == t(n) & col(n) != row(n) & lower.tri(n),
arr.ind=TRUE) )
[1] "B"
I simply do not see my
mistake.
I would rather program a problem correctly that hash through errors in
loop logic.
--
David Winsemius, MD
West Hartford, CT
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