dataframe Spark scala explode json array

Question

Let's say I have a dataframe which looks like this:

+--------------------+--------------------+--------------------------------------------------------------+
|                id  |           Name     |                                                       Payment|
+--------------------+--------------------+--------------------------------------------------------------+
|                1   |           James    |[ {"@id": 1, "currency":"GBP"},{"@id": 2, "currency": "USD"} ]|
+--------------------+--------------------+--------------------------------------------------------------+

And the schema is:

root

|-- id: integer (nullable = true)
|-- Name: string (nullable = true)   
|-- Payment: string (nullable = true)

How can I explode the above JSON array into below:

+--------------------+--------------------+-------------------------------+
|                id  |           Name     |                        Payment|
+--------------------+--------------------+-------------------------------+
|                1   |           James    |   {"@id":1, "currency":"GBP"} |
+--------------------+--------------------+-------------------------------+
|                1   |           James    |   {"@id":2, "currency":"USD"} |
+--------------------+--------------------+-------------------------------+

I've been trying to use the explode functionality like the below, but it's not working. It's giving an error about not being able to explode string types, and that it expects either a map or array. This makes sense given the schema denotes it's a string, rather than an array/map, but I'm not sure how to convert this into an appropriate format.

val newDF = dataframe.withColumn("nestedPayment", explode(dataframe.col("Payment")))

Any help is greatly appreciated!

Answer 1

You'll have to parse the JSON string into an array of JSONs, and then use explode on the result (explode expects an array).

To do that (assuming Spark 2.0.*):

• If you know all Payment values contain a json representing an array with the same size (e.g. 2 in this case), you can hard-code extraction of the first and second elements, wrap them in an array and explode:

  val newDF = dataframe.withColumn("Payment", explode(array(
    get_json_object($"Payment", "$[0]"),
    get_json_object($"Payment", "$[1]")
  )))
  

• If you can't guarantee all records have a JSON with a 2-element array, but you can guarantee a maximum length of these arrays, you can use this trick to parse elements up to the maximum size and then filter out the resulting nulls:

  val maxJsonParts = 3 // whatever that number is...
  val jsonElements = (0 until maxJsonParts)
                       .map(i => get_json_object($"Payment", s"$$[$i]"))
  
  val newDF = dataframe
    .withColumn("Payment", explode(array(jsonElements: _*)))
    .where(!isnull($"Payment"))