removeing only rows/columns with "na" value from square ( symmetrical ) matrix.

On Sun, May 20, 2012 at 10:17 AM, Nevil Amos <nevil.amos at monash.edu> wrote:

I have some square matrices with na values in corresponding rows and
columns.

M<-matrix(1:2,10,10)
M[6,1:2]<-NA
M[10,9]<-NA
M<-as.matrix(as.dist(M))
print (M)

? ?1 2 3 4 5 6 7 8 9 10
1 ? 0 ?2 1 2 1 NA 1 2 ?1 ?2
2 ? 2 ?0 1 2 1 NA 1 2 ?1 ?2
3 ? 1 ?1 0 2 1 ?2 1 2 ?1 ?2
4 ? 2 ?2 2 0 1 ?2 1 2 ?1 ?2
5 ? 1 ?1 1 1 0 ?2 1 2 ?1 ?2
6 ?NA NA 2 2 2 ?0 1 2 ?1 ?2
7 ? 1 ?1 1 1 1 ?1 0 2 ?1 ?2
8 ? 2 ?2 2 2 2 ?2 2 0 ?1 ?2
9 ? 1 ?1 1 1 1 ?1 1 1 ?0 NA
10 ?2 ?2 2 2 2 ?2 2 2 NA ?0


How do I remove just the row/column pair( in this trivial example row 6 and
10 and column 6 and 10) containing the NA values?

so that I end up with all rows/ columns that are not NA - e.g.

?1 2 3 4 5 7 8 9
1 0 2 1 2 1 1 2 1
2 2 0 1 2 1 1 2 1
3 1 1 0 2 1 1 2 1
4 2 2 2 0 1 1 2 1
5 1 1 1 1 0 1 2 1
7 1 1 1 1 1 0 2 1
8 2 2 2 2 2 2 0 1
9 1 1 1 1 1 1 1 0

Try this:

ix <- na.action(na.omit(replace(M, upper.tri(M), 0)))
M[-ix, -ix]