R : Convert nested list into a one level list

Question

I got the following y nested list :

x1=c(12,54,2)
x2=c(2,88,1)
x3=c(4,8)

y=list()
y[[1]]=x1
y[[2]]=list(x2,x3)

y
[[1]]
[1] 12 54  2

[[2]]
[[2]][[1]]
[1]  2 88  1

[[2]][[2]]
[1] 4 8

I would like to extract all elements from this nested list and put them into a one level list, so my expected result should be :

y_one_level_list
[[1]]
[1] 12 54  2

[[2]]
[1]  2 88  1

[[3]]
[1] 4 8

Obviously ma real problem involve a deeper nested list, how would you solve it? I tried rapply but I failed.

@d.b unfortunately, no, I did look this post and it does not produce the expected results. — hans glick, Mar 11 '17 at 19:41
[These solutions](https://stackoverflow.com/questions/48443179/flatten-nested-lists-in-a-list/48443290#48443290) also work and preserve the structure of my data better — Simone, Nov 03 '21 at 08:17

score 18 · Accepted Answer · answered Mar 11 '17 at 19:39

18

Try lapply together with rapply:

lapply(rapply(y, enquote, how="unlist"), eval)

#[[1]]
#[1] 12 54  2

#[[2]]
#[1]  2 88  1

#[[3]]
#[1] 4 8

It does work for deeper lists either.

answered Mar 11 '17 at 19:39

989

12,579
5
31
53

1

Yeaaah It also works, more elegant way to do it thanks – hans glick Mar 11 '17 at 19:43
excellent solution! FYI. https://www.r-bloggers.com/rapply-function-explanation-and-examples/ – Grec001 May 25 '19 at 03:11
what is the `eval` doing at the end? – WestCoastProjects Mar 04 '20 at 17:44
Some explanation would also be nice. What are `enquote` and `eval` @989? – PM0087 Apr 22 '20 at 15:44
`?enquote` states that: `enquote is a simple one-line utility which transforms a call of the form Foo(....) into the call quote(Foo(....))`. Then, `eval(quote(c(4,8)))`, for instance, returns a vector containing `4,8` – 989 Apr 23 '20 at 00:22
Thanks. The other [solutions](https://stackoverflow.com/questions/48443179/flatten-nested-lists-in-a-list) did not work for me – Simone Oct 07 '21 at 06:33

score 8 · Answer 2 · answered Mar 11 '17 at 19:36

8

You can try this:

flatten <- function(lst) {
    do.call(c, lapply(lst, function(x) if(is.list(x)) flatten(x) else list(x)))
}

flatten(y)

#[[1]]
#[1] 12 54  2

#[[2]]
#[1]  2 88  1

#[[3]]
#[1] 4 8

answered Mar 11 '17 at 19:36

Psidom

209,562
33
339
356

1

funny i think this one is simpler. – WestCoastProjects Mar 04 '20 at 17:44

R : Convert nested list into a one level list

2 Answers2

Linked

Related