eitsupi commented on code in PR #14175:
URL: https://github.com/apache/arrow/pull/14175#discussion_r990536980
##########
r/R/dplyr.R:
##########
@@ -182,7 +182,7 @@ dim.arrow_dplyr_query <- function(x) {
# Query on in-memory Table, so evaluate the filter
# Don't need any columns
x <- select.arrow_dplyr_query(x, NULL)
- rows <- nrow(compute.arrow_dplyr_query(x))
+ rows <- nrow(as_arrow_table(x))
Review Comment:
This is because manipulating metadata for a table with no rows will cause
the size to be updated to 0 x 0.
``` r
mtcars |> arrow::arrow_table() |> dplyr::select(NULL) |>
arrow::as_arrow_table()
#> Table
#> 32 rows x 0 columns
#>
#>
#> See $metadata for additional Schema metadata
mtcars |> arrow::arrow_table() |> dplyr::select(NULL) |>
arrow::as_arrow_table() |> dplyr::ungroup()
#> Table
#> 0 rows x 0 columns
#>
#>
#> See $metadata for additional Schema metadata
```
<sup>Created on 2022-10-07 with [reprex
v2.0.2](https://reprex.tidyverse.org)</sup>
I don't know if this (handling of tables with no rows) is a problem.
A table with 0 rows and multiple columns appears to be quite exceptional,
since creating a table from a data frame with no rows results in 0 x 0.
``` r
mtcars |> dplyr::select(NULL) |> arrow::arrow_table()
#> Table
#> 0 rows x 0 columns
#>
#>
#> See $metadata for additional Schema metadata
```
<sup>Created on 2022-10-07 with [reprex
v2.0.2](https://reprex.tidyverse.org)</sup>
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