Unnesting tibble with zero rows removes unnested column

[frederikziebell]

Here is an example that produces the problem:

df <- tibble(
 a = list(c(1, 2), 3),
 b = c(4,5)
)

df %>%
  unnest(a) %>%
  colnames
# [1] "b" "a"

df %>%
  filter(b==1) %>%
  unnest(a) %>%
  colnames
# [1] "b"

If the special case occurs that the tibble being unnested has no rows, all code acting on the unnested column breaks.

[krlmlr]

Thanks, confirmed with both the CRAN version and 581c2c0.

[khailper]

I'll try this.

[hadley]

A bit more of a reprex to help me understand the problem:

library(tidyr)

df <- tibble::tibble(a = list(1), y = 1)
df %>% unnest(a) %>% str()
#> Classes 'tbl_df', 'tbl' and 'data.frame':    1 obs. of  2 variables:
#>  $ y: num 1
#>  $ a: num 1
df %>% .[0, ] %>% unnest(a) %>% str()
#> Classes 'tbl_df', 'tbl' and 'data.frame':    0 obs. of  1 variable:
#>  $ y: num

^{Created on 2019-01-22 by the reprex package (v0.2.1.9000)}

[hadley]

I think the root cause is actually this:

list_col_type(character())
#> [1] "data.frame"