Let's say I have a list like this:
x = list(list(1,2), list(3,4), list(5,6))
I would like a list that contains only the first elements of the nested list. I can do this by returning another list like so
x1 = lapply(x, function(l) l[[1]])
Is there shortcut notation for this?
We can use pluck from rvest which selects 1st element from each nested list
rvest::pluck(x, 1)
#[[1]]
#[1] 1
#[[2]]
#[1] 3
#[[3]]
#[1] 5
Note that this gives different result with pluck from purrr which selects 1st element (x[[1]])
purrr::pluck(x, 1)
#[[1]]
#[1] 1
#[[2]]
#[1] 2
Not exactly a short notation, but this can also be done with a fold:
Reduce(function(a, b) c(a, b[1]), x, init = c())
# [[1]]
# [1] 1
#
# [[2]]
# [1] 3
#
# [[3]]
# [1] 5