Find index position in nested lists for match

Question

I want to find the Indexes of the match of a nested list and a target value (11).

Data:

f <- list(
  list(1, 2, 3),
  list(4, 5, list(8, list(11, 12)))
)

Desired Output for target value = 11.:

c(2, 3, 2, 1)

Printed:

 f
[[1]]
[[1]][[1]]
[1] 1

[[1]][[2]]
[1] 2

[[1]][[3]]
[1] 3


[[2]]
[[2]][[1]]
[1] 4

[[2]][[2]]
[1] 5

[[2]][[3]]
[[2]][[3]][[1]]
[1] 8

[[2]][[3]][[2]]
--->>>  [[2]][[3]][[2]][[1]]  <<<----
-->>>> [1] 11 <<<----

[[2]][[3]][[2]][[2]]
[1] 12

What i tried:

match with unlist(data), Looking for Parameter in which() and Looking into arrInd().

I would avoid running multiple for loops in R. It would be better to do all loops in C, C++,... Before implementing it myself i wanted to check if i am missing a function.

Answer 1

foo = function(x, sep = ".") {
    names(x) = paste0(seq_along(x))
    while(any(sapply(x, class) == "list")) {
        ind = sapply(x, class) == "list"
        temp = unlist(x[ind], recursive = FALSE)
        names(temp) = paste0(rep(names(x)[ind], lengths(x[ind])),
                             sep,
                             sequence(lengths(x[ind])))
        x = c(x[!ind], temp)
    }
    return(x)
}
f2 = foo(f)
names(which(unlist(f2) == 11))
#[1] "2.3.2.1"

Answer 2

This can also be done with rrapply in the rrapply-package (extended version of base rapply). The condition argument decides to which elements f should be applied, and the .xpos argument in the f function evaluates to the position of the element in the nested list. how = "flatten" discards all list elements that do not satisfy condition and returns a flattened list:

library(rrapply)

rrapply(f, condition = function(x) x == 11, f = function(x, .xpos) .xpos, how = "flatten")
#> [[1]]
#> [1] 2 3 2 1