Github user marmbrus commented on a diff in the pull request:
https://github.com/apache/spark/pull/9531#discussion_r44202704
--- Diff: sql/core/src/main/scala/org/apache/spark/sql/DataFrame.scala ---
@@ -1478,18 +1478,54 @@ class DataFrame private[sql](
/**
* Returns the first `n` rows in the [[DataFrame]].
+ *
+ * Running take requires moving data into the application's driver
process, and doing so on a
+ * very large dataset can crash the driver process with OutOfMemoryError.
+ *
* @group action
* @since 1.3.0
*/
def take(n: Int): Array[Row] = head(n)
/**
+ * Returns the first `n` rows in the [[DataFrame]] as a list.
+ *
+ * Running take requires moving data into the application's driver
process, and doing so on a
+ * very large dataset can crash the driver process with OutOfMemoryError.
+ *
+ * @group action
+ * @since 1.6.0
+ */
+ def takeAsList(n: Int): java.util.List[Row] =
java.util.Arrays.asList(take(n) : _*)
+
+ /**
* Returns an array that contains all of [[Row]]s in this [[DataFrame]].
+ *
+ * Running collect requires moving all the data into the application's
driver process, and
+ * doing so on a very large dataset can crash the driver process with
OutOfMemoryError.
+ *
+ * For Java API, use [[collectAsList]].
+ *
* @group action
* @since 1.3.0
*/
def collect(): Array[Row] = collect(needCallback = true)
+ /**
+ * Returns a Java list that contains all of [[Row]]s in this
[[DataFrame]].
+ *
+ * Running collect requires moving all the data into the application's
driver process, and
+ * doing so on a very large dataset can crash the driver process with
OutOfMemoryError.
+ *
+ * @group action
+ * @since 1.3.0
+ */
+ def collectAsList(): java.util.List[Row] = withCallback("collectAsList",
this) { _ =>
--- End diff --
oh hmm, not in the PR, but we should add `withCallback` to dataset too.
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