replace list element with another list element based on name

Question

I have two list m.list and the other r.list. The m.list has NA values. For those that have NA values, I would like to replace it with elements from r.list. The problem is when I use replace function in R it is taking the index of the r.list and returns a incorrect value. Below is reproducible examples. IS there a way to replace value of one list based on the element name from another list?

m.list <- list(a= 1,b=NA,c=3,d=NA)

r.list <- list(a= 4,d=8,c=9)

mr.list <- replace(m.list, which(is.na(m.list)), r.list[which(is.na(m.list))])

Here is the output that I get b should be NA and d should be 8:

> mr.list
$a
[1] 1

$b
[1] 8

$c
[1] 3

$d
NULL

here is the desired output:

$a
[1] 1

$b
[1] NA

$c
[1] 3

$d
[1] 8

Answer 1

Here is an option with modifyList

modifyList(m.list, r.list[intersect(names(r.list), names(which(is.na(m.list))))])
#$a
#[1] 1

#$b
#[1] NA

#$c
#[1] 3

#$d
#[1] 8

If we split the code, the idea is to find the names in 'm.list' where the value is missing and that is also found in 'r.list' (intersect), then with modifyList replace the values in 'm.list' with the subset of 'r.list'

nm1 <- intersect(names(r.list), names(which(is.na(m.list))))
modifyList(m.list, r.list[nm1])