search for: replaceinlist

Dear all, I have a list like this: l <- list(list(a=1,b=NULL), list(a=2,b=2)) I want to find out the elements with value of NULL and replace them with NA. The actual case has a very long list, so manually find out and replace them is not an option. I can use for loop to do this, but I want to know if there is vectorized way (or other ways) to do it? Thanks -- Wincent Rong-gui HUANG Doctoral