Prevent unlist to drop NULL values

Question

I have a vector of lists and I use unlist on them. Some of the elements in the vectors are NULL and unlist seems to be dropping them.<

Answer 1

The issue here is that you can't have NULL in the middle of a vector. For example:

> c(1,NULL,3)
[1] 1 3

You can have NA in the middle though. You could could convert it to character and then back to numeric, which automatically converts the NULL values to NA (with a warning):

> b <- as.numeric(as.character(a))
Warning message:
NAs introduced by coercion 

then put the names back in, because they've been dropped by the previous operation:

> names(b) <- names(a)
> b
p1 p2 p1 p2 p1 p2 p1 p2 
2  5  3  4 NA NA  4  5 `