[GitHub] [arrow] boshek commented on a diff in pull request #12818: ARROW-16038: [R] different behavior from dplyr when mutate's `.keep` option is set

[GitBox <gi...@apache.org>]

boshek commented on code in PR #12818:
URL: https://github.com/apache/arrow/pull/12818#discussion_r844464046


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r/R/dplyr-mutate.R:
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@@ -112,7 +113,15 @@ mutate.Dataset <- mutate.ArrowTabular <- mutate.RecordBatchReader <- mutate.arro
 
 transmute.arrow_dplyr_query <- function(.data, ...) {
   dots <- check_transmute_args(...)
-  dplyr::mutate(.data, !!!dots, .keep = "none")
+  has_null <- vapply(dots, quo_is_null, logical(1))
+  .data <- dplyr::mutate(.data, !!!dots, .keep = "none")
+  if (is_empty(dots) | any(has_null)) return(.data)
+
+  ## keeping with: https://github.com/tidyverse/dplyr/issues/6086
+  cur_exprs <- vapply(dots, as_label, character(1))
+  new_col_names <- names(dots)
+  transmute_order <- ifelse(nzchar(new_col_names), new_col_names, cur_exprs)

Review Comment:
   Very open to other approaches but the dplyr implementation of `transmute` return the columns in the order they are given in the function call which is now distinct from `mutate(..., .keep = "none")`.  So this was what i came up with to preserve that order. But there possibly could be a better way to capture order? 



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