UDF function on ArrayType column that contains StringType elements

Question

I need a udf function to input array column of dataframe and perform equality check of two string elements in it. My dataframe has a schema like this.

ID	date	options
1	2021-01-06	['red', 'green']
2	2021-01-07	['Blue', 'Blue']
3	2021-01-08	['Blue', 'Yellow']
4	2021-01-09	nan

I have tried this :

def equality_check(options: list):
  try:
   if options[0] == options[1]:
     return 1
   else:
     return 0
  except:
     return -1

equality_udf = f.udf(equality_check, t.IntegerType())

But it was throwing out of index error. I am confident that options column is array of strings. the expectation is this:

ID	date	options	equality_check
1	2021-01-06	['red', 'green']	0
2	2021-01-07	['Blue', 'Blue']	1
3	2021-01-08	['Blue', 'Yellow']	0
4	2021-01-09	nan	-1

blackbishop · Accepted Answer · 2021-02-09 05:59:30Z

You can check if the options list is defined or its length is inferior to 2 instead of using try/except. Here's a working example:

from pyspark.sql import functions as F
from pyspark.sql.types import IntegerType

data = [
    (1, "2021-01-06", ['red', 'green']),
    (2, "2021-01-07", ['Blue', 'Blue']),
    (3, "2021-01-08", ['Blue', 'Yellow']),
    (4, "2021-01-09", None),
]
df = spark.createDataFrame(data, ["ID", "date", "options"])

def equality_check(options: list):
    if not options or len(options) < 2:
        return -1

    return int(options[0] == options[1])

equality_udf = F.udf(equality_check, IntegerType())

df1 = df.withColumn("equality_check", equality_udf(F.col("options")))
df1.show()

#+---+----------+--------------+--------------+
#| ID|      date|       options|equality_check|
#+---+----------+--------------+--------------+
#|  1|2021-01-06|  [red, green]|             0|
#|  2|2021-01-07|  [Blue, Blue]|             1|
#|  3|2021-01-08|[Blue, Yellow]|             0|
#|  4|2021-01-09|          null|            -1|
#+---+----------+--------------+--------------+

However, I advise you to not use UDF as you can do the same using only built-in functions :

df1 = df.withColumn(
    "equality_check",
    F.when(F.size(F.col("options")) < 2, -1)
        .when(F.col("options")[0] == F.col("options")[1], 1)
        .otherwise(0)
)

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