From cd9f49a2aed3799964976ead06080a0f7044a0c3 Mon Sep 17 00:00:00 2001 From: hyukjinkwon Date: Sat, 13 Jan 2018 16:13:44 +0900 Subject: [PATCH] [SPARK-22980][PYTHON][SQL] Clarify the length of each series is of each batch within scalar Pandas UDF ## What changes were proposed in this pull request? This PR proposes to add a note that saying the length of a scalar Pandas UDF's `Series` is not of the whole input column but of the batch. We are fine for a group map UDF because the usage is different from our typical UDF but scalar UDFs might cause confusion with the normal UDF. For example, please consider this example: ```python from pyspark.sql.functions import pandas_udf, col, lit df = spark.range(1) f = pandas_udf(lambda x, y: len(x) + y, LongType()) df.select(f(lit('text'), col('id'))).show() ``` ``` +------------------+ |(text, id)| +------------------+ | 1| +------------------+ ``` ```python from pyspark.sql.functions import udf, col, lit df = spark.range(1) f = udf(lambda x, y: len(x) + y, "long") df.select(f(lit('text'), col('id'))).show() ``` ``` +------------------+ |(text, id)| +------------------+ | 4| +------------------+ ``` ## How was this patch tested? Manually built the doc and checked the output. Author: hyukjinkwon Closes #20237 from HyukjinKwon/SPARK-22980. --- python/pyspark/sql/functions.py | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/python/pyspark/sql/functions.py b/python/pyspark/sql/functions.py index 733e32bd825b0..e1ad6590554cf 100644 --- a/python/pyspark/sql/functions.py +++ b/python/pyspark/sql/functions.py @@ -2184,6 +2184,11 @@ def pandas_udf(f=None, returnType=None, functionType=None): | 8| JOHN DOE| 22| +----------+--------------+------------+ + .. note:: The length of `pandas.Series` within a scalar UDF is not that of the whole input + column, but is the length of an internal batch used for each call to the function. + Therefore, this can be used, for example, to ensure the length of each returned + `pandas.Series`, and can not be used as the column length. + 2. GROUP_MAP A group map UDF defines transformation: A `pandas.DataFrame` -> A `pandas.DataFrame`