jonkeane commented on a change in pull request #11373:
URL: https://github.com/apache/arrow/pull/11373#discussion_r727130827
##########
File path: r/R/dataset-scan.R
##########
@@ -143,6 +139,26 @@ Scanner$create <- function(dataset,
#' @export
names.Scanner <- function(x) names(x$schema)
+#' @export
+head.Scanner <- function(x, n = 6L, ...) {
+ assert_that(n > 0) # For now
+ dataset___Scanner__head(x, n)
+}
+
+#' @export
+tail.Scanner <- function(x, n = 6L, ...) {
+ assert_that(n > 0) # For now
Review comment:
Out of curiosity: what's the "For now" in reference to?
##########
File path: r/R/dataset-scan.R
##########
@@ -143,6 +139,26 @@ Scanner$create <- function(dataset,
#' @export
names.Scanner <- function(x) names(x$schema)
+#' @export
+head.Scanner <- function(x, n = 6L, ...) {
+ assert_that(n > 0) # For now
+ dataset___Scanner__head(x, n)
+}
+
+#' @export
+tail.Scanner <- function(x, n = 6L, ...) {
+ assert_that(n > 0) # For now
Review comment:
Ah I see now it wouldn't work with the implementation down there.
##########
File path: r/R/dplyr.R
##########
@@ -162,22 +162,35 @@ as.data.frame.arrow_dplyr_query <- function(x, row.names
= NULL, optional = FALS
#' @export
head.arrow_dplyr_query <- function(x, n = 6L, ...) {
- # TODO (ARROW-13893): refactor
- out <- head.Dataset(x, n, ...)
- restore_dplyr_features(out, x)
+ out <- as_adq(x)
+ out$head <- n
+ collapse.arrow_dplyr_query(out)
}
#' @export
tail.arrow_dplyr_query <- function(x, n = 6L, ...) {
- # TODO (ARROW-13893): refactor
- out <- tail.Dataset(x, n, ...)
- restore_dplyr_features(out, x)
+ out <- as_adq(x)
Review comment:
Do we need this `as_adq()` here? It should be harmless / a no-op, but it
should always go through the `inherits(.data, "arrow_dplyr_query")` path, no?
##########
File path: r/R/query-engine.R
##########
@@ -18,7 +18,12 @@
do_exec_plan <- function(.data) {
plan <- ExecPlan$create()
final_node <- plan$Build(.data)
- tab <- plan$Run(final_node)$read_table()
+ tab <- plan$Run(final_node)
+
+ # TODO (ARROW-14289): make the head/tail methods return RBR not Table
+ if (inherits(tab, "RecordBatchReader")) {
+ tab <- tab$read_table()
+ }
Review comment:
🤔 this might be useful in / simplify the `to_arrow()` branch
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