map_df() can't make a list-column

[jennybc]

library(purrr)
library(tibble)
x <- list(list(a = "a",
               n = 1:2),
          list(a = "A",
               n = 3:7))
x %>% {
  tibble(
    a = map_chr(., "a"),
    n = map(., "n")
  )
}
#> # A tibble: 2 × 2
#>       a         n
#>   <chr>    <list>
#> 1     a <int [2]>
#> 2     A <int [5]>
x %>% map_df(`[`, c("a", "n"))
#> Error: incompatible sizes (1 != 2)

[hadley]

Moved to dplyr; I'm not 100% sure this should work, but it's worth thinking about.