Add a layer to a list following names

Question

I have this one layer list :

have <- list("a" = 1, "b.a" = 2, "b.b" = 3)

I need this 2 layers list :

need <- list("a" = 1, "b" = list("a" = 2, "b" = 3))

Would be even better if the solution could be recursive. The goal is to structurate the data as it could be parsed to some Json file for example.

Thank you !

Answer 1

This recursive function should do the trick:

f <- function(obj) {
  nms <- lapply(strsplit(names(obj), '\\.'), function(x){
    if(length(x) == 1) x else c(x[1], paste(x[-1], collapse = '.'))
  })
  first_nms <- sapply(nms, `[`, 1)
  last_nms <- sapply(nms, `[`, -1)
  un_nms <- unique(first_nms)
  setNames(lapply(un_nms, function(x) {
    o <- unname(obj[first_nms %in% x])
    if(length(o) == 1) unlist(o) else
      f(setNames(o, last_nms[first_nms %in% x]))
    }), un_nms)
}

Testing, we have:

have <- list("a" = 1, "b.a" = 2, "b.b" = 3)

f(have)
#> $a
#> [1] 1
#> 
#> $b
#> $b$a
#> [1] 2
#> 
#> $b$b
#> [1] 3

And we can see it works on deeply nested lists:

f(list(a = 1, b.a = 2, b.b = 3, c.a.a = 4, c.a.b = 5, c.b.a = 6, c.b.b = 7))
#> $a
#> [1] 1
#> 
#> $b
#> $b$a
#> [1] 2
#> 
#> $b$b
#> [1] 3
#> 
#> 
#> $c
#> $c$a
#> $c$a$a
#> [1] 4
#> 
#> $c$a$b
#> [1] 5
#> 
#> 
#> $c$b
#> $c$b$a
#> [1] 6
#> 
#> $c$b$b
#> [1] 7