BigQuery - Convert result into array of JSONs

Question

Let say, that I have the following input data:

id | val1 | val2
 1 |  1v1 |  1v2
 1 |  1v3 |  2v4
 2 |  2v1 |  2v2

What I would like to achieve in the output:

id | json
 1 | [{"val1":"1v1","val2":"1v2"}, {"val1":"1v3","val2":"1v4"}]
 2 | [{"val1":"2v1","val2":"2v2"}]

So all results grouped by id, in JSON array. Multiple rows per ID produces multiple structs in the JSON array.
As the first step I tried to group rows into JSONs using TO_JSON_STRING function, and ended with code like this:

WITH Input AS ( 
  SELECT id, val1, val2
  from My_Table
)
SELECT
  t.id,
  TO_JSON_STRING(t) AS json_row
FROM Input AS t

But it also puts id into the target JSON, which I want to avoid.
Any help or hints how to get desirable result from BigQuery will be greatly appreciated.

Answer 1

See the following code:

with data as (
  select 1 as id, '1v1' as val1, '1v2' as val2 union all 
  select 1, '1v3', '2v4' union all 
  select 2, '2v1', '2v2'
),
grouped as (
  select id, array_agg(struct(val1,val2)) x
  from data
  group by 1
)
select id, to_json_string(x) as json 
from grouped