[jira] [Created] (ARROW-16833) [R] how to enforce type conversion in open_dataset()

["Zsolt Kegyes-Brassai (Jira)" <ji...@apache.org>]

Zsolt Kegyes-Brassai created ARROW-16833:
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             Summary: [R] how to enforce type conversion in open_dataset()
                 Key: ARROW-16833
                 URL: https://issues.apache.org/jira/browse/ARROW-16833
             Project: Apache Arrow
          Issue Type: Improvement
    Affects Versions: 8.0.0
            Reporter: Zsolt Kegyes-Brassai


Here is a small example:

{{}}
{code:java}
library(arrow)
df_numbers <- tibble::tibble(number = c(1,2,3,"error", 4, 5, NA, 6))
str(df_numbers)
#> tibble [8 x 1] (S3: tbl_df/tbl/data.frame)
#>  $ number: chr [1:8] "1" "2" "3" "error" ...
write_parquet(df_numbers, "numbers.parquet")
open_dataset("numbers.parquet") 
#> FileSystemDataset with 1 Parquet file
#> number: string
open_dataset("numbers.parquet", schema(number = int8())) |> dplyr::collect()
#> Error in `dplyr::collect()`:
#> ! Invalid: Failed to parse string: 'error' as a scalar of type int8

{code}
The expected result is having an input column of integers; where the non-integer values are converted to NAs.

How this type conversion can be enforced using schema definition in in the  {{{}open_dataset(){}}}? 

Rationale: I would like to include this in a code chunk  which imports a csv dataset and saves to parquet dataset (open_dataset -> write_dataset); where the type conversion based on a preset schema would be done at the same time.  And all these steps without loading all the data in memory.



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