So here is the test case from the commit adding the first/last methods here:
https://github.com/apache/spark/pull/10957/commits/defcc02a8885e884d5140b11705b764a51753162
+ test("last/first with ignoreNulls") {
+ val nullStr: String = null
+ val df = Seq(
+ ("a", 0, nullStr),
+ ("a", 1, "x"),
+ ("a", 2, "y"),
+ ("a", 3, "z"),
+ ("a", 4, nullStr),
+ ("b", 1, nullStr),
+ ("b", 2, nullStr)).
+ toDF("key", "order", "value")
+ val window = Window.partitionBy($"key").orderBy($"order")
+ checkAnswer(
+ df.select(
+ $"key",
+ $"order",
+ first($"value").over(window),
+ first($"value", ignoreNulls = false).over(window),
+ first($"value", ignoreNulls = true).over(window),
+ last($"value").over(window),
+ last($"value", ignoreNulls = false).over(window),
+ last($"value", ignoreNulls = true).over(window)),
+ Seq(
+ Row("a", 0, null, null, null, null, null, null),
+ Row("a", 1, null, null, "x", "x", "x", "x"),
+ Row("a", 2, null, null, "x", "y", "y", "y"),
+ Row("a", 3, null, null, "x", "z", "z", "z"),
+ Row("a", 4, null, null, "x", null, null, "z"),
+ Row("b", 1, null, null, null, null, null, null),
+ Row("b", 2, null, null, null, null, null, null)))
+ }
I would expect the correct results to be as follows instead of what is used
above. Shouldn't we always return the first or last value in the partition
based on the ordering? It looks something else is going on... can someone
explain?
+ Seq(
+ Row("a", 0, null, null, "x", null, null, "z"),
+ Row("a", 1, null, null, "x", null, null, "z"),
+ Row("a", 2, null, null, "x", null, null, "z"),
+ Row("a", 3, null, null, "x", null, null, "z"),
+ Row("a", 4, null, null, "x", null, null, "z"),
+ Row("b", 1, null, null, null, null, null, null),
+ Row("b", 2, null, null, null, null, null, null)))
From: Alexander Peletz [mailto:alexand...@slalom.com]
Sent: Wednesday, August 17, 2016 11:57 AM
To: user <user@spark.apache.org>
Subject: pyspark.sql.functions.last not working as expected
Hi,
I am using Spark 2.0 and I am getting unexpected results using the last()
method. Has anyone else experienced this? I get the sense that last() is
working correctly within a given data partition but not across the entire RDD.
First() seems to work as expected so I can work around this by having a window
that is in reverse order and use first() instead of last() but it would be
great if last() actually worked.
Thanks,
Alexander
Alexander Peletz
Consultant
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alexand...@slalom.com<mailto:alexand...@slalom.com>
