Spark 3.4.0 - Getting Empty DataFrame after Filtering on UDF with Dynamic Input
I'm maintaining legacy code that I'm reviewing some code and I've been struggling with this for a few days now and could really use some help. I'm currently working with Apache Spark 3.4.0 and working with an scenario where I apply a User Defined Function (UDF) to filter a DataFrame, but the result is an empty DataFrame even though I expect to get some rows. I have a scenario where I want to filter out rows based on a dynamic condition derived from another DataFrame. Here’s the relevant snippet of my code: ```python from pyspark.sql import SparkSession from pyspark.sql.functions import udf from pyspark.sql.types import BooleanType spark = SparkSession.builder.appName('FilterExample').getOrCreate() # Sample DataFrame data = [('Alice', 1), ('Bob', 2), ('Cathy', 3)] df = spark.createDataFrame(data, ['name', 'id']) # Create a second DataFrame for filtering criteria filter_data = [('Bob',), ('Cathy',)] filter_df = spark.createDataFrame(filter_data, ['name']) # UDF to check if name is in the filter DataFrame filter_names = filter_df.select('name').rdd.flatMap(lambda x: x).collect() @udf(BooleanType()) def is_in_filter(name): return name in filter_names # Attempting to filter the DataFrame using the UDF filtered_df = df.filter(is_in_filter(df.name)) filtered_df.show() ``` When I run this code, I get the following output: ``` +-----+---+ | name| id| +-----+---+ +-----+---+ ``` I expected to see rows for 'Bob' and 'Cathy', but the result is empty. I suspect it might be related to how I'm collecting the filter names or how the UDF is being executed across the partitions. I've also tried debugging by printing `filter_names` and it correctly lists `['Bob', 'Cathy']`. I'm wondering if there are any best practices for filtering with UDFs like this, or if there's a better way to achieve this without running into issues. Any insights would be greatly appreciated! How would you solve this? I'm working on a application that needs to handle this. I've been using Python for about a year now. Any feedback is welcome! I'm developing on macOS with Python. Hoping someone can shed some light on this. The stack includes Python and several other technologies. Am I missing something obvious?