Suppose we have list l which is a list of lists.
a <- list(c(1,2,3))
b <- list(c(4,5,6), c(7,8,9))
c <- list(c(10,11,12), c(13,14,15), c(16,17,18))
l <- list(a, b, c)
So l is a list of lists, where each of those lists itself contains at least one list.
Question
How can I make a function which can extract all the lowest level lists into a single list of lists?
# Goal
list(c(1,2,3), c(4,5,6), c(7,8,9), c(10,11,12), c(13,14,15), c(16,17,18))
Notes:
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The example is a minimal reproducible example for which it would be possible to hard-code a solution, but it is important that the solution generalise, since the real problem has tens-of-thousands of lists each containing unknown numbers of lists – so a hard-coded solution definitely won’t scale!
-
I hope to find a solution in base R, if possible.
A few things I’ve tried so far
Some unsuccessful attempts, mostly using sapply() and unlist():
sapply(l, function(x) { unlist(x) })
# [[1]]
# [1] 1 2 3
#
# [[2]]
# [1] 4 5 6 7 8 9
#
# [[3]]
# [1] 10 11 12 13 14 15 16 17 18
unlist(a)
# [1] 1 2 3
# unlist() seems to combine the elements of multiple lists into one list (not desired here)..
unlist(b)
# [1] 4 5 6 7 8 9
I thought the recursive = FALSE argument looked promising, but unfortunately I couldn’t get it to do what I wanted either:
unlist(b, recursive = FALSE)
# [1] 4 5 6 7 8 9
>Solution :
Use unlist, non-recursive on your initial list.
unlist(l, recursive=FALSE)
# [[1]]
# [1] 1 2 3
#
# [[2]]
# [1] 4 5 6
#
# [[3]]
# [1] 7 8 9
#
# [[4]]
# [1] 10 11 12
#
# [[5]]
# [1] 13 14 15
#
# [[6]]
# [1] 16 17 18