[R] Implement dplyr::across() inside summarise()

[asfimport]

ARROW-11699 adds the ability to call dplyr::across() inside dplyr::mutate(). Once this is merged, we should also add the ability to do so within dplyr::summarise().

Reporter: Nicola Crane / @thisisnic
Assignee: Nicola Crane / @thisisnic

Related issues:

• [R] Implement dplyr::across() inside mutate() (is blocked by)

PRs and other links:

• GitHub Pull Request #14042

_{Note: This issue was originally created as ARROW-17362. Please see the migration documentation for further details.}

[asfimport]

Nicola Crane / @thisisnic:
Issue resolved by pull request 14042
#14042