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https://issues.apache.org/jira/browse/ARROW-15879?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Jonathan Keane updated ARROW-15879:
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Fix Version/s: (was: 9.0.0)
> [R] passing a schema calls open_dataset to fail on hive-partitioned csv files
> -----------------------------------------------------------------------------
>
> Key: ARROW-15879
> URL: https://issues.apache.org/jira/browse/ARROW-15879
> Project: Apache Arrow
> Issue Type: Bug
> Components: R
> Affects Versions: 7.0.0, 7.0.1
> Reporter: Carl Boettiger
> Priority: Major
> Labels: pull-request-available
> Time Spent: 40m
> Remaining Estimate: 0h
>
> Consider this reprex:
>
> Create a dataset with hive partitions in csv format with write_dataset() (so
> cool!):
>
> {code:java}
> library(arrow)
> library(dplyr)
> path <- fs::dir_create("tmp")
> mtcars %>% group_by(gear) %>% write_dataset(path, format="csv")## works fine,
> even with 'collect()'
> ds <- open_dataset(path, format="csv")## but pass a schema, and things fail
> df <- open_dataset(path, format="csv", schema = ds$schema, skip_rows=1)
> df %>% collect()
> {code}
> In the first call to open_dataset, we don't pass a schema and things work as
> expected.
> However, csv files often need a schema to be read in correctly, particularly
> with partitioned data where it is easy to 'guess' the wrong type. Passing
> the schema though confuses open_dataset, because the grouping column
> (partition column) isn't found on the individual files even though it is
> mentioned in the schema!
> Nor can we just omit the grouping column from the schema, since then it is
> effectively lost from the data.
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