val explodedOnceDF = df.select(col("customer_id"),explode("service").as("service"))
val explodedTwiceDF = explodedOnceDF.select(col("customer_id"),explode("service").as("service"))
val requiredOutput = explodedTwiceDF.groupBy("customer_id").agg(collect_list("service").as("service")).select(col("customer_id"),col("service"))