[FIXED] Replace elements in an array with its corresponding number in pyspark

Issue

I have a dataframe shown below:

   +----------+--------------------------------+
   | Index    |           flagArray            |
   +----------+--------------------------------+
   |    1     | ['A','S','A','E','Z','S','S']  | 
   +----------+--------------------------------+
   |    2     | ['A','Z','Z','E','Z','S','S']  |
   +--------- +--------------------------------+

I want to represent array elements with its corresponding numeric values.

     A - 0
     F - 1
     S - 2
     E - 3
     Z - 4

So my output dataframe should look like

   +----------+--------------------------------+--------------------------------+
   | Index    |           flagArray            |           finalArray           |
   +----------+--------------------------------+--------------------------------+
   |    1     | ['A','S','A','E','Z','S','S']  | [0, 2, 0, 3, 4, 2, 2]          | 
   +----------+--------------------------------+--------------------------------+
   |    2     | ['A','Z','Z','E','Z','S','S']  | [0, 4, 4, 3, 4, 2, 2]          |
   +--------- +--------------------------------+--------------------------------+

I have written an udf in pyspark where I am achieving it by writing some if else statements. Is there any better way to handle the same.

Solution

For Spark 2.4+, you can simply use transform function to loop through each element of flagArray array and get its mapping value from a map column that you can create from that mapping using element_at:

mappings = {"A": 0, "F": 1, "S": 2, "E": 3, "Z": 4}
mapping_col = map_from_entries(array(*[struct(lit(k), lit(v)) for k, v in mappings.items()]))

df = df.withColumn("mappings", mapping_col) \
       .withColumn("finalArray", expr(""" transform(flagArray, x -> element_at(mappings, x))""")) \
       .drop("mappings")

df.show(truncate=False)
#+-----+---------------------+---------------------+
#|Index|flagArray            |finalArray           |
#+-----+---------------------+---------------------+
#|1    |[A, S, A, E, Z, S, S]|[0, 2, 0, 3, 4, 2, 2]|
#|2    |[A, Z, Z, E, Z, S, S]|[0, 4, 4, 3, 4, 2, 2]|
#+-----+---------------------+---------------------+

Answered By - blackbishop