ueshin commented on a change in pull request #35191:
URL: https://github.com/apache/spark/pull/35191#discussion_r822010938
##########
File path: python/pyspark/pandas/series.py
##########
@@ -5228,9 +5229,20 @@ def asof(self, where: Union[Any, List]) -> Union[Scalar,
"Series"]:
where = [where]
index_scol = self._internal.index_spark_columns[0]
index_type = self._internal.spark_type_for(index_scol)
+
+ if np.nan in where:
+ # When `where` is np.nan, pandas returns the last index value.
+ last_index =
self._internal.spark_frame.select(F.last(index_scol)).take(1)[0][0]
+ modified_where = [last_index if x is np.nan else x for x in where]
+ else:
+ modified_where = where
+
cond = [
- F.max(F.when(index_scol <= SF.lit(index).cast(index_type),
self.spark.column))
- for index in where
+ F.last(
Review comment:
The document says `F.last` is non-deterministic.
https://github.com/apache/spark/blob/master/python/pyspark/sql/functions.py#L1337-L1340
Even if the dataframe is sorted beforehand, `F.last` will cause a shuffle
because it's an aggregate function, thus the result may be non-deterministic.
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