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https://issues.apache.org/jira/browse/ARROW-16833?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Todd Farmer updated ARROW-16833:
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Component/s: R
> [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
> Components: R
> Affects Versions: 8.0.0
> Reporter: Zsolt Kegyes-Brassai
> Priority: Minor
>
> 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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