tibble() - Constructing a tibble with NULL evaluating expression arguments inconsistent with constructing a tibble with NULL valued arguments.

While debugging a Redditor's question I came across an issue I've distilled here.

library(tibble)
tib_works <- tibble(x = NULL, y = NULL, z = NULL)
tib_fails <- tibble(x = c(), y = c(), z = c())

str(tib_works)
#> tibble [0 x 0] (S3: tbl_df/tbl/data.frame)
#>  Named list()

str(tib_fails)
#> tibble [0 x 3] (S3: tbl_df/tbl/data.frame)
#>  $ x: NULL
#>  $ y: NULL
#>  $ z: NULL

tib_works
#> # A tibble: 0 x 0
tib_fails
#> Error: Internal error in `vec_slice_impl()`: Unexpected `NULL`.

rlang::last_trace()
<error/rlang_error>
Internal error in `vec_slice_impl()`: Unexpected `NULL`.
Backtrace:
     x
  1. +-(function (x, ...) ...
  2. \-pillar:::print.tbl(x)
  3.   +-base::writeLines(format(x, width = width, ..., n = n, n_extra = n_extra))
  4.   +-base::format(x, width = width, ..., n = n, n_extra = n_extra)
  5.   \-pillar:::format.tbl(x, width = width, ..., n = n, n_extra = n_extra)
  6.     \-pillar::tbl_format_setup(x, width = width, ..., n = n, max_extra_cols = n_extra)
  7.       +-pillar:::tbl_format_setup_(x, width, ..., n = n, max_extra_cols = max_extra_cols)
  8.       \-pillar:::tbl_format_setup.tbl(x, width, ..., n = n, max_extra_cols = max_extra_cols)
  9.         \-pillar:::df_head(x, n)
 10.           \-pillar:::vec_head(as.data.frame(x), n)
 11.             \-vctrs::vec_slice(x, seq_len(n))
 12.               \-(function () ...

df1 <- data.frame(x = NULL, y = NULL, z = NULL)
df2 <- data.frame(x = c(), y = c(), z = c())
identical(df1, df2)
#> [1] TRUE

^{Created on 2021-06-13 by the reprex package (v2.0.0)}

Setting aside the larger issues that this is, to say the least, poor form, not doing what they intend, and would invariably lead to other issues immediately thereafter, is this the intended and desired behaviour of tibble()?

A clear analogy here would be to treat this like a patient telling their doctor "it hurts when I do this," and respond, "well, stop doing that! But, in the interest of helping novices should tibble() here:

Throw an error.
Throw a warning.
Behave similarly to data.frame() and produce identical objects in both cases.
Do nothing differently, tibble() is working as intended. This is a PEBCAK situation.

Alternately, should an error be thrown further up the chain somewhere in pillar, perhaps in pillar:::format.tbl() where an error message more relevant to the user's input could be generated?

Thanks, confirmed. We need to fix that. Smaller reprex:

dput(tibble::tibble(x = c(), y = c(), z = c()))
#> structure(list(x = NULL, y = NULL, z = NULL), row.names = integer(0), class = c("tbl_df", 
#> "tbl", "data.frame"))

^{Created on 2021-06-24 by the reprex package (v2.0.0)}

I think tibble:::tibble_quos() needs to compact() away any NULLs that appeared after the eval_tidy() loop (and compact the column names as required). It already seems to skip over them in the loop if they appear after calling eval_tidy(), but they are never removed.

That will catch any NULL values that were "computed", i.e. like c().

If you do that, you might also be able to remove the is.null <- map_lgl(xs, quo_is_null) bit from tibble(), and instead allow that post-loop check to remove both "computed" and explicit NULL columns.

Merge pull request #902 from tidyverse/b-895-900-eval-null

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`tibble()` - Constructing a `tibble` with `NULL` evaluating expression arguments inconsistent with constructing a `tibble` with `NULL` valued arguments. #895

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tibble() - Constructing a tibble with NULL evaluating expression arguments inconsistent with constructing a tibble with NULL valued arguments. #895

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krlmlr commented on Jun 24, 2021

DavisVaughan commented on Jul 1, 2021

github-actions commented on Jul 18, 2022

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`tibble()` - Constructing a `tibble` with `NULL` evaluating expression arguments inconsistent with constructing a `tibble` with `NULL` valued arguments. #895