How to manipulate NULL elements in a nested list?

Question

I have a nested list containing NULL elements, and I\'d like to replace those with something else. For example:

l <- list(
  NULL,
  1,
  list(
    2,
           


        

Answer 1

This is a hack, but as far as hacks go, I think I'm somewhat happy with it.

lna <- eval(parse(text = gsub("NULL", "NA", deparse(l))))

str(lna)
#> List of 3
#> $ : logi NA
#> $ : num 1
#> $ :List of 3
#> ..$ : num 2
#> ..$ : logi NA
#> ..$ :List of 2
#> .. ..$ : num 3
#> .. ..$ : logi NA

Update:

If for some reason you needed "NULL" as a character entry in the list (corner case, much?) you can still use the above hack since it replaces the contents of the string, not the quotes, thus it just requires another step

l2 <- list(
  NULL,
  1,
  list(
    2,
    "NULL",
    list(
      3,
      NULL
    )
  )
)

lna2   <- eval(parse(text = gsub("NULL", "NA", deparse(l2))))
lna2_2 <- eval(parse(text = gsub('\\"NA\\"', '\"NULL\"', deparse(lna2))))

str(lna2_2)
#> List of 3
#> $ : logi NA
#> $ : num 1
#> $ :List of 3
#> ..$ : num 2
#> ..$ : chr "NULL"
#> ..$ :List of 2
#> .. ..$ : num 3
#> .. ..$ : logi NA