使用 UDF 连接 Pyspark 数据框 [英] Pyspark Dataframe Join using UDF
问题描述
我正在尝试为 PySpark 中的两个数据帧(df1 和 df2)创建自定义连接(类似于 this),代码如下所示:
I'm trying to create a custom join for two dataframes (df1 and df2) in PySpark (similar to this), with code that looks like this:
my_join_udf = udf(lambda x, y: isJoin(x, y), BooleanType())
my_join_df = df1.join(df2, my_join_udf(df1.col_a, df2.col_b))
我收到的错误信息是:
java.lang.RuntimeException: Invalid PythonUDF PythonUDF#<lambda>(col_a#17,col_b#0), requires attributes from more than one child
有没有办法编写一个 PySpark UDF 来处理来自两个独立数据帧的列?
Is there a way to write a PySpark UDF that can process columns from two separate dataframes?
推荐答案
Spark 2.2+
你必须使用 crossJoin
或在配置中启用交叉连接:>
You have to use crossJoin
or enable cross joins in the configuration:
df1.crossJoin(df2).where(my_join_udf(df1.col_a, df2.col_b))
Spark 2.0、2.1
下面显示的方法在 Spark 2.x 中不再有效.请参阅 SPARK-19728.
Method shown below doesn't work anymore in Spark 2.x. See SPARK-19728.
Spark 1.x
理论上你可以加入和过滤:
Theoretically you can join and filter:
df1.join(df2).where(my_join_udf(df1.col_a, df2.col_b))
但总的来说,您不应该全部完成.任何不基于等式的 join
都需要一个完整的笛卡尔积(与答案相同),这很少被接受(另见 为什么在 SQL 查询中使用 UDF 会导致笛卡尔积?).
but in general you shouldn't to it all. Any type of join
which is not based on equality requires a full Cartesian product (same as the answer) which is rarely acceptable (see also Why using a UDF in a SQL query leads to cartesian product?).
这篇关于使用 UDF 连接 Pyspark 数据框的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!