Does a multi-value purrr::pluck exist?

Question

Seems like a basic question and perhaps I'm just missing something obvious ... but is there any way to pluck a sublist (with purrr)? More specifically, here's an initial list:

l <- list(a = "foo", b = "bar", c = "baz")

And I want to return a new (sub-)list with only elements a and b. Normally, I'd just do 'base' R sub-listing:

l[c("a", "b")]

But this doesn't provide the nice .default handling of pluck. My understanding is that pluck 'replaces' [[, but is there a purrr equivalent for replacing [?

Answer 1

Similar to jzadra's post, you could also do:

l %>% keep(names(.) %in% c("a","b"))

Answer 2

Here's my take on it. Not based on purrr thus slightly off topic, but compatible with the tidyverse's general interface principle of playing nicely with pipes.

pluck_multiple <- function(x, ...) {
  `[`(x, ...)
}

x <- list(a = 1, b = 2, c = list(x = TRUE, y = FALSE))

pluck_multiple(x, c("a", "b"))
#> $a
#> [1] 1
#> 
#> $b
#> [1] 2
pluck_multiple(x, 2:3)
#> $b
#> [1] 2
#> 
#> $c
#> $c$x
#> [1] TRUE
#> 
#> $c$y
#> [1] FALSE

Answer 3

There's clearly a need for "muti-value pluck". It really comes down to extending flexibility of "pluck" to retrieving multiple values from the same level of list, as described in this github issue. For the example above, you can probably get away with:

> purrr::map(purrr::set_names(c("a", "b")), 
          ~purrr::pluck(l, .x, .default = NA_character_))
#> $a
#> [1] "foo"
#> 
#> $b
#> [1] "bar"

Answer 4

I think that purrr::keep() does what you want.

l %>% keep(names(.) == "a" | names(.) == "b")