[jira] [Created] (ARROW-16575) arrow::write_dataset() does nothing with 0 row dataframes in R

["Adam Black (Jira)" <ji...@apache.org>]

Adam Black created ARROW-16575:
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             Summary: arrow::write_dataset() does nothing with 0 row dataframes in R
                 Key: ARROW-16575
                 URL: https://issues.apache.org/jira/browse/ARROW-16575
             Project: Apache Arrow
          Issue Type: Improvement
         Environment: Mac OS 12.3, R 4.1
            Reporter: Adam Black


In R a dataframe can have 0 rows. It still has column names and types. 

 

Expected behavior of arrow::write_dataset

I would expect that it would be possible to have a FileSystemDataset with zero rows that would contain metadata about the column names and types. arrow::write_dataset would create the FileSystemDataset metadata when given a dataframe with zero rows.

 

Actual behavior

arrow::write_dataset() does nothing when passed a dataframe with zero rows.

 

Reproducible example using the current arrow package on CRAN
{code:java}
arrow::write_dataset(cars, here::here("cars"))
arrow::open_dataset(here::here("cars"))
#> FileSystemDataset with 1 Parquet file
#> speed: double
#> dist: double
#> 
#> See $metadata for additional Schema metadata
file.exists(here::here("cars"))
#> [1] TRUE




df <- cars[cars$speed > 1000, ]
nrow(df)
#> [1] 0
arrow::write_dataset(df, here::here("df"), format = "feather")
arrow::open_dataset(here::here("df"))
#> Error: IOError: Cannot list directory '/private/var/folders/xx/01v98b6546ldnm1rg1_bvk000000gn/T/RtmpGkX0gK/reprex-17c305ed29ad5-nerdy-ram/df'. Detail: [errno 2] No such file or directory
file.exists(here::here("df"))
#> [1] FALSE{code}



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