pdmetcalfe opened a new issue, #50163:
URL: https://github.com/apache/arrow/issues/50163
### Describe the bug, including details regarding any error messages,
version, and platform.
## Description
Three methods in the arrow R package access R metadata using `x$metadata$r`.
Because `$` on a named list uses partial matching, any schema-level metadata
key that starts with `"r"` but is not `"r"` (e.g. `"rachel"`, `"row_count"`,
`"result"`) will be erroneously matched and its value passed to
`apply_arrow_r_metadata()` or used as group var metadata. This causes spurious
`"Invalid metadata$r"` warnings or hard errors depending on the matched value.
The fix in all three locations is to replace `x$metadata$r` with
`x$metadata[["r"]]`.
## Affected code
- `collect.ArrowTabular`: `apply_arrow_r_metadata(df, x$metadata$r)`
- `as.data.frame.ArrowTabular`: `apply_arrow_r_metadata(df, x$metadata$r)`
- `group_vars.ArrowTabular`: `x$metadata$r$attributes$.group_vars`
## Reprex
```r
library(arrow)
library(dplyr)
# Build a table with a schema metadata key that starts with "r" but isn't
"r".
# This can happen when integrating with systems that attach their own
metadata
# (e.g., a key called "rachel", "row_count", "result", etc.).
tbl <- arrow_table(x = 1:3)
tbl_rachel <- tbl$cast(
tbl$schema$WithMetadata(list(rachel = "some_value"))
)
# Confirm that $r partial-matches to $rachel, while [["r"]] correctly
returns NULL
meta <- tbl_rachel$metadata
meta$r # "some_value" <-- partial match: WRONG
meta[["r"]] # NULL <-- exact match: correct
# as.data.frame() spuriously warns "Invalid metadata$r"
as.data.frame(tbl_rachel)
#> Warning message: Invalid metadata$r
# collect() same spurious warning
collect(tbl_rachel)
#> Warning message: Invalid metadata$r
# group_vars() hard errors because it does
x$metadata$r$attributes$.group_vars
# and "$" is invalid on an atomic vector
group_vars(tbl_rachel)
#> Error in x$metadata$r$attributes : $ operator is invalid for atomic
vectors
```
## Expected behaviour
- `as.data.frame()` and `collect()` should return the data without any
warning — there is no `"r"` metadata key, so no R metadata should be applied.
- `group_vars()` should return `character(0)` — there are no group vars
encoded.
## Actual behaviour
- `as.data.frame()` and `collect()` emit a spurious `"Invalid metadata$r"`
warning.
- `group_vars()` throws `"$ operator is invalid for atomic vectors"`.
## Root cause
`schema$metadata` returns a plain R list. R's `$` operator performs partial
matching on lists, so `meta$r` resolves to `meta$rachel` when no exact `"r"`
key exists. The fix is to use `[[` (which never partial-matches) everywhere
`$metadata$r` appears:
```r
# Before (all three methods)
x$metadata$r
# After
x$metadata[["r"]]
```
## Session Info
```
R version 4.6.0 (2026-04-24)
Platform: aarch64-apple-darwin25.4.0
Running under: macOS Tahoe 26.5.1
Matrix products: default
BLAS: /opt/homebrew/Cellar/openblas/0.3.33/lib/libopenblasp-r0.3.33.dylib
LAPACK: /opt/homebrew/Cellar/r/4.6.0/lib/R/lib/libRlapack.dylib; LAPACK
version 3.12.1
locale:
[1] en_GB.UTF-8/en_GB.UTF-8/en_GB.UTF-8/C/en_GB.UTF-8/en_GB.UTF-8
time zone: Europe/London
tzcode source: internal
attached base packages:
[1] stats graphics grDevices utils datasets methods base
other attached packages:
[1] dplyr_1.2.1 arrow_24.0.0
loaded via a namespace (and not attached):
[1] assertthat_0.2.1 R6_2.6.1 bit_4.6.0 tidyselect_1.2.1
[5] magrittr_2.0.5 glue_1.8.1 tibble_3.3.1 pkgconfig_2.0.3
[9] bit64_4.8.2 generics_0.1.4 lifecycle_1.0.5 cli_3.6.6
[13] vctrs_0.7.3 compiler_4.6.0 purrr_1.2.2 pillar_1.11.1
[17] rlang_1.2.0
```
### Component(s)
R
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