How to select multiple lists elements at once by pluck?

[luobbgg]

mm <- list(a = list(1:2), b = list(3:4), d = list(5:6))
nn <- list(a = list(7:8), b = list(9:10), d = list(11:12))
kk <- list(mm, nn)

kk |> map(pluck(2))
[[1]]
[[1]][[1]]
[1] 3 4

[[2]]
[[2]][[1]]
[1] 9 10

If we want to pluck arbitrary list element 2, 3 or more at once with map, like pluck(2:n) didn't work,

or paste("pluck(., ", seq(2:n), ")", collapse = ", ", sep = "") didn't work too,

or paste("pluck(., ", c(2, 3, 5, n), ")", collapse = ", ", sep = "") didn't work too,

how can we do?

We hope the outputs like this

#> List of 2
#>  $ :List of 2
#>   ..$ : int [1:2] 3 4
#>   ..$ : int [1:2] 5 6
#>  $ :List of 2
#>   ..$ : int [1:2] 9 10
#>   ..$ : int [1:2] 11 12
......

Or any other solutions?

Thanks!

[HanOostdijk]

E.g. with

library(purrr)

mm <- list(a = list(1:2), b = list(3:4), d = list(5:6))
nn <- list(a = list(7:8), b = list(9:10), d = list(11:12))
kk <- list(mm, nn)

kk1 <- kk |> purrr::map(~c(pluck(.,2),pluck(.,3))) 
str(kk1)
#> List of 2
#>  $ :List of 2
#>   ..$ : int [1:2] 3 4
#>   ..$ : int [1:2] 5 6
#>  $ :List of 2
#>   ..$ : int [1:2] 9 10
#>   ..$ : int [1:2] 11 12
Created on 2021-09-15 by the reprex package (v2.0.0)

?

[luobbgg]

When use paste in the map with purrr expression, it didn't work

mm <- list(a = list(1:2), b = list(3:4), d = list(5:6))
nn <- list(a = list(7:8), b = list(9:10), d = list(11:12))
kk <- list(mm, nn)

kk |> purrr::map(~c(paste("pluck(., ", seq(2:3), ")", collapse = ", ", sep = "")))

How to figure it out?

[HanOostdijk]

It works for me but I agree that the output is not very interesting.
Please show us the desired output, because you did not mention that before.

[luobbgg]

We modified needs clearly at the top post，thanks to your suggestion.

[HanOostdijk]

I still don't know exactly what you are looking for.
If it only amounts to selecting an 'arbitrary' number of elements then I would use [ ] as given below.
So no solution with pluck !

Explanation:
I thought that the kk2 solution could work, but I saw that the result was different.
In kk3 I corrected for this.

I hope this works for you. If not, let us know.

library(purrr)

mm <- list(a = list(1:2), b = list(3:4), c = list(5:6))
nn <- list(a = list(7:8), b = list(9:10), c = list(11:12))
kk <- list(mm, nn)

# old version
kk1 <- kk |> purrr::map(~c(pluck(.,2),pluck(.,3))) 
str(kk1)
#> List of 2
#>  $ :List of 2
#>   ..$ : int [1:2] 3 4
#>   ..$ : int [1:2] 5 6
#>  $ :List of 2
#>   ..$ : int [1:2] 9 10
#>   ..$ : int [1:2] 11 12

# newer version but different result
kk2 <- kk |> purrr::map( ~(.[c(2,3)]) )
str(kk2)
#> List of 2
#>  $ :List of 2
#>   ..$ b:List of 1
#>   .. ..$ : int [1:2] 3 4
#>   ..$ c:List of 1
#>   .. ..$ : int [1:2] 5 6
#>  $ :List of 2
#>   ..$ b:List of 1
#>   .. ..$ : int [1:2] 9 10
#>   ..$ c:List of 1
#>   .. ..$ : int [1:2] 11 12

# newest version with same result as old version
kk3 <- kk |> purrr::map( ~(do.call(c,.[c(2,3)])) )
str(kk3)
#> List of 2
#>  $ :List of 2
#>   ..$ b: int [1:2] 3 4
#>   ..$ c: int [1:2] 5 6
#>  $ :List of 2
#>   ..$ b: int [1:2] 9 10
#>   ..$ c: int [1:2] 11 12

# same with three 'plucks'
kk4 <- kk |> purrr::map( ~(do.call(c,.[c(2,3,1)])) )
str(kk4)
#> List of 2
#>  $ :List of 3
#>   ..$ b: int [1:2] 3 4
#>   ..$ c: int [1:2] 5 6
#>   ..$ a: int [1:2] 1 2
#>  $ :List of 3
#>   ..$ b: int [1:2] 9 10
#>   ..$ c: int [1:2] 11 12
#>   ..$ a: int [1:2] 7 8
Created on 2021-09-17 by the reprex package (v2.0.0)

[arthur.t]

map(kk, ~.[2:3])

or

map(kk, magrittr::extract, 2:3)

I don't understand what you're trying to do with the paste here:

kk |> purrr::map(~c(paste("pluck(., ", seq(2:3), ")", collapse = ", ", sep = "")))