unite fails with internal error if the columns don't exist

[jwilliman]

While using tidyr::unite on a list of dataframes I came across the following error. I'm only reporting it because it asked me to!

The list of dataframes was messy, so I was looking for a way of combining columns that may or may not exist. I'd be happy for unite to throw a warning, or error, to tell me that there were no input columns selected.

tidyr::unite(mtcars, "hello", contains("missing_column"))
#> Error in `df_append()`:
#> ! `after` must be a whole number, not an integer `NA`.
#> ℹ This is an internal error that was detected in the tidyr package.
#>   Please report it at <https://github.com/tidyverse/tidyr/issues> with a reprex
#>   (<https://tidyverse.org/help/>) and the full backtrace.
#> Backtrace:
#>     ▆
#>  1. ├─tidyr::unite(mtcars, "hello", contains("missing_column"))
#>  2. └─tidyr:::unite.data.frame(mtcars, "hello", contains("missing_column"))
#>  3.   └─tidyr:::df_append(after = after)
#>  4.     └─tidyr:::check_number_whole(after, min = 0L, max = n, .internal = TRUE)
#>  5.       └─tidyr:::.rlang_types_check_number(...)
#>  6.         └─tidyr (local) .stop(x, what, ...)
#>  7.           └─tidyr:::stop_input_type(...)
#>  8.             └─rlang::abort(message, ..., call = call, arg = arg)

^{Created on 2023-08-31 with reprex v2.0.2}

[DavisVaughan]

I think its a bug on our end, thanks!

[GuiFabre]

Hello, I get the same error. Not to mention that the error is not consistent. Sometimes it works, sometimes not.

The problem might come from the fact it use unite( -1 , [...] ) instead of unite( 2:last_col() , [...] ) or something.

Best :

[jospueyo]

Same error here. I came because the error told me to do so.

library(tidyverse)

df <- tibble(
  a_1 = 3,
  a_2 = 4
)

df |> 
  unite(b, starts_with("b"))
#> Error in `df_append()`:
#> ! `after` must be a whole number, not an integer `NA`.
#> ℹ This is an internal error that was detected in the tidyr package.
#>   Please report it at <https://github.com/tidyverse/tidyr/issues> with a reprex
#>   (<https://tidyverse.org/help/>) and the full backtrace.
#> Backtrace:
#>     ▆
#>  1. ├─tidyr::unite(df, b, starts_with("b"))
#>  2. └─tidyr:::unite.data.frame(df, b, starts_with("b"))
#>  3.   └─tidyr:::df_append(after = after)
#>  4.     └─tidyr:::check_number_whole(after, min = 0L, max = n, .internal = TRUE)
#>  5.       └─tidyr:::.rlang_types_check_number(...)
#>  6.         └─tidyr (local) .stop(x, what, ...)
#>  7.           └─tidyr:::stop_input_type(...)
#>  8.             └─rlang::abort(message, ..., call = call, arg = arg)

^{Created on 2024-02-12 with reprex v2.0.2}

[DavisVaughan]

Dup of #1548