traversc opened a new issue, #51695:
URL: https://github.com/apache/arrow/issues/51695
### Describe the bug, including details regarding any error messages,
version, and platform.
### Describe the bug, including details regarding any error messages,
version, and platform.
Double-valued attributes, including date-times, do not round-trip through
Arrow's R metadata. No warning is raised. (Tested on arrow 25.0.1, R 4.6.1,
Linux.)
```r
library(arrow)
options(digits.secs = 6)
df <- data.frame(x = 1:3)
attr(df, "updated") <- as.POSIXct("2026-10-02 14:30:15.987654321", tz =
"UTC")
f <- tempfile(fileext = ".parquet")
write_parquet(df, f)
back <- read_parquet(f)
attr(df, "updated")
#> [1] "2026-10-02 14:30:15.987654 UTC"
attr(back, "updated")
#> [1] "2026-10-02 14:30:15.987653 UTC"
identical(attr(back, "updated"), attr(df, "updated"))
#> [1] FALSE
```
### Suggested fix
Fortuitously, R already has an exact variant of the ASCII format, so the fix
is simple and fully backwards compatible.
Arrow uses `R_pstream_ascii_format` (`ascii = TRUE` in `base::serialize`).
Instead use `R_pstream_asciihex_format` (`ascii = NA`).
```r
out <- serialize(safe_r_metadata(x, on_save = TRUE), NULL, ascii = NA)
```
The hex format means that doubles are written out in hex instead of decimal.
Either way, the output still starts with `"A"` (arrow's check) and base
`unserialize()` reads it fine, so the reader needs no change and previous
versions work with the output.
### Component(s)
R
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