vec_rbind coerces POSIXlt to POSIXct

[Moohan]

I was using purrr::list_rbind() but it seems like the behaviour/bug is coming from vctrs... When combining dataframes with a POSIXlt they are coerced to POSIXct, which is not expected.

Reprex:

library(tibble)

df_list <- list(
  df1 = tibble(
    dates_lt = as.POSIXlt(Sys.time()),
    dates_ct = as.POSIXct(Sys.time())
    ),
  df2 = tibble(
    dates_lt = as.POSIXlt(Sys.time() - 60),
    dates_ct = as.POSIXct(Sys.time() - 60)
  )
)

str(purrr::list_rbind(df_list))
#> tibble [2 × 2] (S3: tbl_df/tbl/data.frame)
#>  $ dates_lt: POSIXct[1:2], format: "2024-04-24 15:02:37" "2024-04-24 15:01:37"
#>  $ dates_ct: POSIXct[1:2], format: "2024-04-24 15:02:37" "2024-04-24 15:01:37"
str(dplyr::bind_rows(df_list))
#> tibble [2 × 2] (S3: tbl_df/tbl/data.frame)
#>  $ dates_lt: POSIXct[1:2], format: "2024-04-24 15:02:37" "2024-04-24 15:01:37"
#>  $ dates_ct: POSIXct[1:2], format: "2024-04-24 15:02:37" "2024-04-24 15:01:37"
str(vctrs::vec_rbind(!!!df_list))
#> tibble [2 × 2] (S3: tbl_df/tbl/data.frame)
#>  $ dates_lt: POSIXct[1:2], format: "2024-04-24 15:02:37" "2024-04-24 15:01:37"
#>  $ dates_ct: POSIXct[1:2], format: "2024-04-24 15:02:37" "2024-04-24 15:01:37"

[DavisVaughan]

We push very hard towards POSIXct over POSIXlt, because the internal representation of POSIXlt is quite convoluted and memory heavy. See also #1576 (comment).

We made a design decision long ago that <POSIXlt> + <POSIXlt> = <POSIXct> is the best way to push the more "standard" date-time class of POSIXct, even if that feels slightly weird from a purity standpoint.

If you really really want to avoid that, then you will likely have to use something other than vctrs or the tooling that builds on it to retain POSIXlt.