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https://issues.apache.org/jira/browse/ARROW-16783?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17551580#comment-17551580
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Nicola Crane commented on ARROW-16783:
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Agree that (1) is great as that error message is very misleading in this case
and the {{tryCatch()}} is too broad.
Not sure about pushing the check down as here we explicitly reference the
parameter named `dataset` for the error message to make sense, though then if
we find a way around that, then sure! I see there's a PR open, so let's
continue this discussion there!
> [R] write_dataset fails with an uninformative message when duplicated column
> names
> ----------------------------------------------------------------------------------
>
> Key: ARROW-16783
> URL: https://issues.apache.org/jira/browse/ARROW-16783
> Project: Apache Arrow
> Issue Type: Improvement
> Components: R
> Affects Versions: 8.0.0
> Reporter: Andy Teucher
> Priority: Major
> Labels: pull-request-available
> Time Spent: 40m
> Remaining Estimate: 0h
>
> {{write_dataset()}} fails when the object being written has duplicated column
> names. This is probably reasonable behaviour, but the error message is
> misleading:
> {code:r}
> library(arrow, warn.conflicts = FALSE)
> df <- data.frame(
> id = c("a", "b", "c"),
> x = 1:3,
> x = 4:6,
> check.names = FALSE
> )
> write_dataset(df, "df")
> #> Error: 'dataset' must be a Dataset, RecordBatch, Table, arrow_dplyr_query,
> or data.frame, not "data.frame"
> {code}
> [{{write_dataset()}} calls {{as_adq()}} inside a {{tryCatch()}}
> statement|https://github.com/apache/arrow/blob/0d5cf1882228624271062e6c19583c8b0c361a20/r/R/dataset-write.R#L146-L160],
> so any error from {{as_adq()}} is swallowed and the error emitted is about
> the class of the object.
> The real error comes from here:
> {code:r}
> arrow:::as_adq(df)
> #> Error in `arrow_dplyr_query()`:
> #> ! Duplicated field names
> #> ✖ The following field names were found more than once in the data: "x"
> {code}
> I'm not sure what your preferred fix is here... two options that come to mind
> are:
> 1. Explicitly check for compatible classes before calling {{as_adq()}}
> instead of using {{tryCatch()}}, allowing `as_adq()` to emit its own errors.
> OR
> 2. Check for duplicate column names before the {{tryCatch}} block
> My thought is that option 1 is better, as option 2 means that checking for
> duplicates would happen twice (once inside {{write_dataset()}} and once again
> inside {{{}as_adq(){}}}).
> I'm happy to work a fix if you like!
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