How to identify which columns are not “NA” per row in a matrix?

Question

I have a matrix with 12 rows and 77 columns, but to simply lets use:

p <- matrix(NA,5,7)  
p[1,2]<-0.3  
p[1,3]<-0.5  
p[2,4]<-0.9  
p[2,7]<-0.4