Github user HyukjinKwon commented on a diff in the pull request:
https://github.com/apache/spark/pull/20400#discussion_r165254262
--- Diff: python/pyspark/sql/functions.py ---
@@ -809,6 +809,48 @@ def ntile(n):
return Column(sc._jvm.functions.ntile(int(n)))
+@since(2.3)
+def unboundedPreceding():
+ """
+ Window function: returns the special frame boundary that represents
the first row
+ in the window partition.
+
+ >>> df = spark.createDataFrame([(5,)])
+ >>> df.select(unboundedPreceding()).columns[0]
+ 'UNBOUNDED PRECEDING'
--- End diff --
Shall we just put these tests as separate tests in `tests.py`? I don't
think this is quite useful as an example in doc to be honest ..
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