ianmcook commented on a change in pull request #9586:
URL: https://github.com/apache/arrow/pull/9586#discussion_r588596519
##########
File path: r/R/dplyr.R
##########
@@ -539,6 +537,13 @@ mutate.arrow_dplyr_query <- function(.data,
if (inherits(results[[new_var]], "try-error")) {
msg <- paste('Expression', as_label(exprs[[i]]), 'not supported in
Arrow')
return(abandon_ship(call, .data, msg))
+ } else if (is_dataset && !inherits(results[[new_var]], "Expression")) {
+ # We need some wrapping to handle literal values
+ if (length(results[[new_var]]) != 1) {
+ msg <- paste0('In ', new_var, " = ", as_label(exprs[[i]]), ", only
values of size one are recycled")
Review comment:
If you `mutate(NULL)` or `transmute(NULL)` it gets caught by this and
gives the message:
```
Error: In NULL = NULL, only values of size one are recycled
Call collect() first to pull data into R.
```
We should handle that case separately and make it behave the same as a
no-argument `mutate()` or `transmute()` (that is, return all the columns or no
columns respectively)
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