Pyspark Converting An Array Of Struct Into String

I have the following dataframe in Pyspark +----+-------+-----+ |name|subject|score| +----+-------+-----+ | Tom| math|

Solution 1:

Per your Update and comment, for Spark 2.4.0+, here is one way to stringify an array of structs with Spark SQL builtin functions: transform and array_join:

>>> df.printSchema()
root
 |-- name: string (nullable = true)
 |-- score_list: array (nullable = true)
 |    |-- element: struct (containsNull = true)
 |    |    |-- subject: string (nullable = true)
 |    |    |-- score: integer (nullable = true)

>>> df.show(2,0)
+----+---------------------------+
|name|score_list                 |
+----+---------------------------+
|Tom |[[math, 90], [physics, 70]]|
|Amy |[[math, 95]]               |
+----+---------------------------+

>>> df1.selectExpr(
        "name"
      , """
         array_join(
             transform(score_list, x -> concat('(', x.subject, ', ', x.score, ')'))
           , ' | '
         ) AS score_list
        """
).show(2,0)

+----+--------------------------+
|name|score_list                |
+----+--------------------------+
|Tom |(math, 90) | (physics, 70)|
|Amy |(math, 95)                |
+----+--------------------------+

Where:

1. Use transform() to convert array of structs into array of strings. for each array element (the struct x), we use concat('(', x.subject, ', ', x.score, ')') to convert it into a string.
2. Use array_join() to join all array elements(StringType) with | , this will return the final string

Solution 2:

The duplicates I linked don't exactly answer your question, since you're combining multiple columns. Nevertheless you can modify the solutions to fit your desired output quite easily.

Just replace the struct with concat_ws. Also use concat to add an opening and closing parentheses to get the output you desire.

from pyspark.sql.functions import concat, concat_ws, lit

df = df.groupBy('name')\
    .agg(
        concat_ws(
            " | ", 
            collect_list(
                concat(lit("("), concat_ws(", ", 'subject', 'score'), lit(")"))
            )
        ).alias('score_list')
    )
df.show(truncate=False)

#+----+--------------------------+
#|name|score_list                |
#+----+--------------------------+
#|Tom |(math, 90) | (physics, 70)|
#|Amy |(math, 95)                |
#+----+--------------------------+

Note that since the comma appears in the score_list column, this value will be quoted when you write to csv if you use the default arguments.

For example:

df.coalesce(1).write.csv("test.csv")

Would produce the following output file:

Tom,"(math, 90) | (physics, 70)"
Amy,"(math, 95)"