[GitHub] [spark] beliefer commented on a change in pull request #29899: [SPARK-33020][PYTHON] Add nth_value as a PySpark function

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

beliefer commented on a change in pull request #29899:
URL: https://github.com/apache/spark/pull/29899#discussion_r496355785



##########
File path: python/pyspark/sql/functions.py
##########
@@ -934,6 +934,25 @@ def lead(col, offset=1, default=None):
     return Column(sc._jvm.functions.lead(_to_java_column(col), offset, default))
 
 
+@since(3.1)
+def nth_value(col, offset, ignoreNulls=False):
+    """
+    Window function: returns the value that is the `offset`\\th row of the window frame
+    (counting from 1), and `null` if the size of window frame is less than `offset` rows.
+
+    It will return the `offset`\\th non-null value it sees when `ignoreNulls` is set to
+    true. If all values are null, then null is returned.
+
+    This is equivalent to the nth_value function in SQL.
+
+    :param col: name of column or expression
+    :param offset: number of row to use as the value
+    :param ignoreNulls: default value

Review comment:
       an optional specification that indicates the NthValue should skip null values in the determination of which row to use.

##########
File path: python/pyspark/sql/functions.py
##########
@@ -934,6 +934,25 @@ def lead(col, offset=1, default=None):
     return Column(sc._jvm.functions.lead(_to_java_column(col), offset, default))
 
 
+@since(3.1)
+def nth_value(col, offset, ignoreNulls=False):
+    """
+    Window function: returns the value that is the `offset`\\th row of the window frame

Review comment:
       `\\th`?




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