Here's my code:

m <- matrix(c(1:5,NA,7,7,NA),
nrow=3,ncol=3,byrow=T)
print(m)
for ( i in 1:dim(m)[[1]] ) {
mm <- sort(m[i,],na.last=c(NA,NA,T)[[i]])
for ( j in 1:(length(mm)-1) ) {
if ( mm[[j]]==mm[[j+1]] ) {
cat(i,j,mm[[j]],fill=T)
}
}
}

On executing this I get an error:

"Error in if (mm[[j]] == mm[[j + 1]]) { : missing value where TRUE/FALSE needed "