The you probably want to create a normal function as opposed to UDF.
A UDF takes your function and applies it on each element in the column one
after the other. You can think of it as working on the result of a loop
iterating on the column.
pyspark.sql.function.regexp_replace receives a column and applies the regex on
each element to create a new column.
You can do it in one of two ways:
The first is using a udf in which case you shouldn’t use the
pyspark.sql.functions.regex but instead use standard python regex.
The second is to simply apply the column changes one after the other in a
function. This should be something like:
def my_f(target_col):
for match,repl in regexp_list:
target_col = regexp_replace(target_col, match,
repl)
return target_col
and then use it with:
Test_data.select(my_f(test_data.name))
The second option is more correct and should provide better performance.
From: Perttu Ranta-aho [mailto:ranta...@iki.fi]
Sent: Thursday, November 17, 2016 1:50 PM
To: user@spark.apache.org
Subject: Re: Nested UDFs
Hi,
My example was little bogus, my real use case is to do multiple regexp
replacements so something like:
def my_f(data):
for match, repl in regexp_list:
data = regexp_replace(match, repl, data)
return data
I could achieve my goal by mutiple .select(regexp_replace()) lines, but one UDF
would be nicer.
-Perttu
to 17. marraskuuta 2016 klo 9.42 Mendelson, Assaf
<assaf.mendel...@rsa.com<mailto:assaf.mendel...@rsa.com>> kirjoitti:
Regexp_replace is supposed to receive a column, you don’t need to write a UDF
for it.
Instead try:
Test_data.select(regexp_Replace(test_data.name<http://test_data.name>, ‘a’, ‘X’)
You would need a Udf if you would wanted to do something on the string value of
a single row (e.g. return data + “bla”)
Assaf.
From: Perttu Ranta-aho [mailto:ranta...@iki.fi<mailto:ranta...@iki.fi>]
Sent: Thursday, November 17, 2016 9:15 AM
To: user@spark.apache.org<mailto:user@spark.apache.org>
Subject: Nested UDFs
Hi,
Shouldn't this work?
from pyspark.sql.functions import regexp_replace, udf
def my_f(data):
return regexp_replace(data, 'a', 'X')
my_udf = udf(my_f)
test_data = sqlContext.createDataFrame([('a',), ('b',), ('c',)], ('name',))
test_data.select(my_udf(test_data.name<http://test_data.name>)).show()
But instead of 'a' being replaced with 'X' I get exception:
File
".../spark-2.0.2-bin-hadoop2.7/python/lib/pyspark.zip/pyspark/sql/functions.py",
line 1471, in regexp_replace
jc = sc._jvm.functions.regexp_replace(_to_java_column(str), pattern,
replacement)
AttributeError: 'NoneType' object has no attribute '_jvm'
???
-Perttu
