Reduce List but avoid Null variables

Question

Given a list with a null element:

l<-list(x=1,b=2,c=NULL)

How can I Reduce the list using '+' addition but avoid adding the NULL value? I tried

Reduce(l,"+",null.rm=T)

but I don't think its got null.rm. Any efficient way of solving this?

Thanks

Answer 1

You can do this with Filter.

Reduce('+', Filter(Negate(is.null), l))

This is also equivalent to tail(cumsum(Filter(Negate(is.null), l)), 1) or just good old-fashioned do.call(sum, l).