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From "Nicholas Chammas (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (SPARK-18866) Codegen fails with cryptic error if regexp_replace() output column is not aliased
Date Tue, 03 Jan 2017 21:26:58 GMT

    [ https://issues.apache.org/jira/browse/SPARK-18866?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15796227#comment-15796227
] 

Nicholas Chammas commented on SPARK-18866:
------------------------------------------

Could be. I guess the issue of aliasing somehow masks the codegen bug with escaping the slash?

> Codegen fails with cryptic error if regexp_replace() output column is not aliased
> ---------------------------------------------------------------------------------
>
>                 Key: SPARK-18866
>                 URL: https://issues.apache.org/jira/browse/SPARK-18866
>             Project: Spark
>          Issue Type: Bug
>          Components: PySpark, SQL
>    Affects Versions: 2.0.2, 2.1.0
>         Environment: Java 8, Python 3.5
>            Reporter: Nicholas Chammas
>            Priority: Minor
>
> Here's a minimal repro:
> {code}
> import pyspark
> from pyspark.sql import Column
> from pyspark.sql.functions import regexp_replace, lower, col
> def normalize_udf(column: Column) -> Column:
>     normalized_column = (
>         regexp_replace(
>             column,
>             pattern='[\s]+',
>             replacement=' ',
>         )
>     )
>     return normalized_column
> if __name__ == '__main__':
>     spark = pyspark.sql.SparkSession.builder.getOrCreate()
>     raw_df = spark.createDataFrame(
>         [('          ',)],
>         ['string'],
>     )
>     normalized_df = raw_df.select(normalize_udf('string'))
>     normalized_df_prime = (
>         normalized_df
>         .groupBy(sorted(normalized_df.columns))
>         .count())
>     normalized_df_prime.show()
> {code}
> When I run this I get:
> {code}
> ERROR CodeGenerator: failed to compile: org.codehaus.commons.compiler.CompileException:
File 'generated.java', Line 80, Column 130: Invalid escape sequence
> {code}
> Followed by a huge barf of generated Java code, _and then the output I expect_. (So despite
the scary error, the code actually works!)
> Can you spot the error in my code?
> It's simple: I just need to alias the output of {{normalize_udf()}} and all is forgiven:
> {code}
> normalized_df = raw_df.select(normalize_udf('string').alias('string'))
> {code}
> Of course, it's impossible to tell that from the current error output. So my *first question*
is: Is there some way we can better communicate to the user what went wrong?
> Another interesting thing I noticed is that if I try this:
> {code}
> normalized_df = raw_df.select(lower('string'))
> {code}
> I immediately get a clean error saying:
> {code}
> py4j.protocol.Py4JError: An error occurred while calling z:org.apache.spark.sql.functions.lower.
Trace:
> py4j.Py4JException: Method lower([class java.lang.String]) does not exist
> {code}
> I can fix this by building a column object:
> {code}
> normalized_df = raw_df.select(lower(col('string')))
> {code}
> So that raises *a second problem/question*: Why does {{lower()}} require that I build
a Column object, whereas {{regexp_replace()}} does not? The inconsistency adds to the confusion
here.



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