[GitHub] [spark] itholic commented on a change in pull request #35191: [SPARK-37491][PYTHON]Fix Series.asof for unsorted values

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

itholic commented on a change in pull request #35191:
URL: https://github.com/apache/spark/pull/35191#discussion_r798208506



##########
File path: python/pyspark/pandas/series.py
##########
@@ -5228,22 +5228,128 @@ 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)
+
+        # e.g where = [10, 20]
+        # In the comments below , will explain how the dataframe will look after transformations.
+        # e.g pd.Series([2, 1, np.nan, 4], index=[10, 20, 30, 40], name="Koalas")
+
+        column_prefix_constant = "col_"
         cond = [
-            F.max(F.when(index_scol <= SF.lit(index).cast(index_type), self.spark.column))
-            for index in where
+            F.when(
+                index_scol <= SF.lit(index).cast(index_type),
+                F.struct(
+                    F.lit(column_prefix_constant + str(index) + "_" + str(idx)).alias("identifier"),
+                    self.spark.column.alias("col_value"),
+                ),
+            ).alias(column_prefix_constant + str(index) + "_" + str(idx))

Review comment:
       Can we make `column_prefix_constant + str(index) + "_" + str(idx)`  as variable and reuse here and there ??

##########
File path: python/pyspark/pandas/series.py
##########
@@ -5228,22 +5228,128 @@ 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)
+
+        # e.g where = [10, 20]
+        # In the comments below , will explain how the dataframe will look after transformations.
+        # e.g pd.Series([2, 1, np.nan, 4], index=[10, 20, 30, 40], name="Koalas")
+
+        column_prefix_constant = "col_"
         cond = [
-            F.max(F.when(index_scol <= SF.lit(index).cast(index_type), self.spark.column))
-            for index in where
+            F.when(
+                index_scol <= SF.lit(index).cast(index_type),
+                F.struct(
+                    F.lit(column_prefix_constant + str(index) + "_" + str(idx)).alias("identifier"),
+                    self.spark.column.alias("col_value"),
+                ),
+            ).alias(column_prefix_constant + str(index) + "_" + str(idx))

Review comment:
       I think we can simply use `F.last` with `ignorenulls=True` instead of `F.max` ??
   (https://spark.apache.org/docs/3.1.1/api/python/reference/api/pyspark.sql.functions.last.html)
   
   e.g.
   ```python
           cond = [
               F.last(F.when(index_scol <= SF.lit(index).cast(index_type), self.spark.column), ignorenulls=True)
               for index in where
       ]
   ```
   
   It returns the last non-null value from given column.




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