How to map object/json array in Snowflake SQL / DBT Macro?

Question

id	some_attribute	json_array
1	"abc"	[ { attr: 'apple'}, { attr: 'banana' } ]

How to get the get rid of attr in json_array so that the table results into something like table below?

id	some_attribute	string_array
1	"abc"	[ 'apple', 'banana' ]

Use case is during the cleaning stage of the data to make further processing and analysis simpler in later stages of the pipeline.

Thx for the help!

Answer 1

One option is to FLATTEN the json array, then construct the string array from the values.

For example

WITH data AS(
  SELECT 1 id, 'abc' as some_attribute
, [{ 'attr': 'apple'}, { 'attr': 'banana' } ] as json_array
)
SELECT 
  id
, some_attribute
, ARRAY_AGG(value:attr::string) WITHIN GROUP( ORDER BY index) as string_array
FROM
  data
, TABLE(FLATTEN(input => json_array))
GROUP BY
  id
, some_attribute

which returns

ID|SOME_ATTRIBUTE|STRING_ARRAY      |
--+--------------+------------------+
 1|abc           |["apple","banana"]|

Answer 2

Another option is to create a JavaScript UDF. For example

CREATE OR REPLACE FUNCTION ARRAY_JSON_VALUES("a" ARRAY, "attr" STRING) 
RETURNS ARRAY 
LANGUAGE JAVASCRIPT RETURNS NULL ON NULL INPUT IMMUTABLE
AS 
$$ 
  return a.map(e => e[attr]);
$$

then

WITH data AS(
  SELECT 1 id, 'abc' as some_attribute, [{ 'attr': 'apple'}, { 'attr': 'banana' } ] as json_array
)
SELECT 
  id
, some_attribute
, ARRAY_JSON_VALUES(json_array,'attr') as string_array
FROM
  data

again returns

ID|SOME_ATTRIBUTE|STRING_ARRAY      |
--+--------------+------------------+
 1|abc           |["apple","banana"]|