galachad opened a new issue, #44524:
URL: https://github.com/apache/arrow/issues/44524
### Describe the bug, including details regarding any error messages,
version, and platform.
When we write the parquet using arrow, we lost information that the data
frame is `data.frame`.
```
arrow::write_parquet(iris, "iris.parquet")
```
When we read `iris.parquet` it's read as tbl by default.
```r
arrow::read_parquet("iris.parquet")
class(arrow::read_parquet("iris.parquet"))
# [1] "tbl_df" "tbl" "data.frame"
```
This bug was introduced in https://github.com/apache/arrow/issues/34775
The class `data.frame` is removed in `.serialize_arrow_r_metadata` function.
https://github.com/apache/arrow/blame/7ef5437e23bd7d7571a0c7a7fc0c5d3634816802/r/R/metadata.R#L25
```r
prop <- arrow::ParquetFileReader$create(
"iris.parquet",
props = arrow::ParquetArrowReaderProperties$create()
)
prop$GetSchema()$metadata$r$attributes$class
# NULL
```
When the parquet is saved, the attributes were removed.
Workaround:
1) Apply extra class to `data.frame`
```r
new_iris <- iris
class(new_iris) <- c("custom.data.frame", "data.frame")
arrow::write_parquet(new_iris, "iris.parquet")
prop <- arrow::ParquetFileReader$create(
"iris.parquet",
props = arrow::ParquetArrowReaderProperties$create()
)
prop$GetSchema()$metadata$r$attributes$class
# [1] "custom.data.frame" "data.frame"
```
2) Apply the metadata properties manually
Bug description:
When we remove `data.frame` class attribute, we read parquet by default as
tibble. In my opinion it's not expected behavior as when we write `data.frame`
we should read `data.frame`.
### Component(s)
R
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