Pyspark: Convert column to lowercase

Question

I want to convert the values inside a column to lowercase. Currently if I use the lower() method, it complains that column objects are not callable. Since there's a function called lower() in SQL, I assume there's a native Spark solution that doesn't involve UDFs, or writing any SQL.

Answer 1

Import lower alongside col:

from pyspark.sql.functions import lower, col 

Combine them together using lower(col("bla")). In a complete query:

spark.table('bla').select(lower(col('bla')).alias('bla')) 

which is equivalent to the SQL query

SELECT lower(bla) AS bla FROM bla 

To keep the other columns, do

spark.table('foo').withColumn('bar', lower(col('bar'))) 

Needless to say, this approach is better than using a UDF because UDFs have to call out to Python (which is a slow operation, and Python itself is slow), and is more elegant than writing it in SQL.

Answer 2

You can use a combination of concat_ws and split

from pyspark.sql.functions import *  df.withColumn('arr_str', lower(concat_ws('::','arr'))).withColumn('arr', split('arr_str','::')).drop('arr_str')