python - How to zip two array columns in Spark SQL

Question

I have a Pandas dataframe. I have tried to join two columns containing string values into a list first and then using zip, I joined each element of the list with '_'. My data set is like below:

df['column_1']: 'abc, def, ghi'
df['column_2']: '1.0, 2.0, 3.0'

I wanted to join these two columns in a third column like below for each row of my dataframe.

df['column_3']: [abc_1.0, def_2.0, ghi_3.0]

I have successfully done so in python using the code below but the dataframe is quite large and it takes a very long time to run it for the whole dataframe. I want to do the same thing in PySpark for efficiency. I have read the data in spark dataframe successfully but I'm having a hard time determining how to replicate Pandas functions with PySpark equivalent functions. How can I get my desired result in PySpark?

df['column_3'] = df['column_2']
for index, row in df.iterrows():
  while index < 3:
    if isinstance(row['column_1'], str):      
      row['column_1'] = list(row['column_1'].split(','))
      row['column_2'] = list(row['column_2'].split(','))
      row['column_3'] = ['_'.join(map(str, i)) for i in zip(list(row['column_1']), list(row['column_2']))]

I have converted the two columns to arrays in PySpark by using the below code

from pyspark.sql.types import ArrayType, IntegerType, StringType
from pyspark.sql.functions import col, split

crash.withColumn("column_1",
    split(col("column_1"), ",s*").cast(ArrayType(StringType())).alias("column_1")
)
crash.withColumn("column_2",
    split(col("column_2"), ",s*").cast(ArrayType(StringType())).alias("column_2")
)

Now all I need is to zip each element of the arrays in the two columns using '_'. How can I use zip with this? Any help is appreciated.

Answer 1

A Spark SQL equivalent of Python's would be pyspark.sql.functions.arrays_zip:

pyspark.sql.functions.arrays_zip(*cols)

Collection function: Returns a merged array of structs in which the N-th struct contains all N-th values of input arrays.

So if you already have two arrays:

from pyspark.sql.functions import split

df = (spark
    .createDataFrame([('abc, def, ghi', '1.0, 2.0, 3.0')])
    .toDF("column_1", "column_2")
    .withColumn("column_1", split("column_1", "s*,s*"))
    .withColumn("column_2", split("column_2", "s*,s*")))

You can just apply it on the result

from pyspark.sql.functions import arrays_zip

df_zipped = df.withColumn(
  "zipped", arrays_zip("column_1", "column_2")
)

df_zipped.select("zipped").show(truncate=False)

+------------------------------------+
|zipped                              |
+------------------------------------+
|[[abc, 1.0], [def, 2.0], [ghi, 3.0]]|
+------------------------------------+

Now to combine the results you can transform (How to use transform higher-order function?, TypeError: Column is not iterable - How to iterate over ArrayType()?):

df_zipped_concat = df_zipped.withColumn(
    "zipped_concat",
     expr("transform(zipped, x -> concat_ws('_', x.column_1, x.column_2))")
) 

df_zipped_concat.select("zipped_concat").show(truncate=False)

+---------------------------+
|zipped_concat              |
+---------------------------+
|[abc_1.0, def_2.0, ghi_3.0]|
+---------------------------+

Note:

Higher order functions transform and arrays_zip has been introduced in Apache Spark 2.4.