ARROW-15123: [R] CSV dataset file header read in as data

[thisisnic]

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[github-actions]

https://issues.apache.org/jira/browse/ARROW-15123

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[paleolimbot]

Just some tiny comments!

[jonkeane]

This is great, thank you! A few comments:

We have the following in the read_csv_arrow() docs, should we have something in the dataset docs for that as well? Or a link back to these?

#' Note that if you are specifying column names, whether by `schema` or
#' `col_names`, and the CSV file has a header row that would otherwise be used
#' to idenfity column names, you'll need to add `skip = 1` to skip that row.

This is well beyond the scope of this ticket / jira, but this got me thinking about it: we wouldn't be able to support someone reading in a csv that has headers in one file ("the first" one in their conception, though I admit we don't (purposefully!) consistently read them in one order). This might be something worth mentioning in our docs (or the cookbook) that if you're going to cut up a file using head/tail/awk from one giant csv to many smaller ones, you're best off dropping the headers too (or including them in every new file)

[thisisnic]

@jonkeane Yeah, I think the documentation could be expanded generally - should be covered in the PR here #12083 and this topic generally should absolutely be covered in the cookbook.

[nealrichardson]

if you're going to cut up a file using head/tail/awk from one giant csv to many smaller ones

We should actually advise against that entirely: use open_dataset() %>% write_dataset() instead and partition meaningfully.

[jonkeane]

We should actually advise against that entirely: use open_dataset() %>% write_dataset() instead and partition meaningfully.

Yes, absolutely. I meant more: if someone has found themselves in that situation we should warn about that (and suggest this as a better alternative)

[thisisnic]

The cookbook has this ticket open for adding something on doing open_dataset()...write_dataset(): apache/arrow-cookbook#130.

Any more changes needed @jonkeane or can this be merged?

[ursabot]

Benchmark runs are scheduled for baseline = 0b95b62 and contender = 4582713. 4582713 is a master commit associated with this PR. Results will be available as each benchmark for each run completes.
Conbench compare runs links:
[Finished ⬇️0.0% ⬆️0.0%] ec2-t3-xlarge-us-east-2
[Failed ⬇️0.0% ⬆️0.0%] ursa-i9-9960x
[Finished ⬇️0.26% ⬆️0.0%] ursa-thinkcentre-m75q
Supported benchmarks:
ec2-t3-xlarge-us-east-2: Supported benchmark langs: Python. Runs only benchmarks with cloud = True
ursa-i9-9960x: Supported benchmark langs: Python, R, JavaScript
ursa-thinkcentre-m75q: Supported benchmark langs: C++, Java