Postgres query to resample data to a specific interval (based on something from SO, but adapted use only one table)

resample.psql

SELECT a.user_id, b.balance, d.as_of_date
FROM   (
   SELECT d AS as_of_date
   FROM   generate_series(timestamp '2015-12-29', '2016-01-10', interval '1 hour') d
) d
JOIN LATERAL (
   select user_id, as_of_date 
   from balances 
   where as_of_date <= d.as_of_date 
   order by as_of_date 
   limit 1
) a ON true
LEFT JOIN LATERAL (
   SELECT user_id, balance
   FROM   balances
   WHERE  user_id = a.user_id
   AND    as_of_date <= d.as_of_date
   ORDER  BY as_of_date DESC
   LIMIT  1
) b ON true
ORDER  BY a.user_id, d.as_of_date;