clickhouse user cpu calculation

sample.sql

create temporary table cputime (dt Date, ts Int8, cpu Int8, user_id Int8);

insert into cputime values 
  ('2019-01-01', 1, 0, 1), ('2019-01-01', 2, 1, 1), ('2019-01-01', 3, 1, 1),
  ('2019-01-01', 4, 0, 1), ('2019-01-01', 5, 2, 1), ('2019-01-01', 6, 3, 1),
  ('2019-01-01', 1, 0, 2), ('2019-01-01', 2, 4, 2), ('2019-01-01', 3, 5, 2),
  ('2019-01-01', 4, 0, 2), ('2019-01-01', 5, 8, 2), ('2019-01-01', 6, 15, 2),
  ('2019-01-01', 7, 5, 2), ('2019-01-01', 8, 8, 2), ('2019-01-01', 9, 8, 2);

select 
    user_id,
    groupArray(cpu) as arr_cpu,
    arrayDifference(arr_cpu) as arr_cpu_diff,
    arraySum(
      arrayFilter(
        x -> x>0,
        arr_cpu_diff
      )
    ) cpu_incorrect,
    arrayMap(
      (x, y) -> if(y >= 0, y, x),
      arr_cpu,
      arr_cpu_diff
    ) as vals,
    arraySum(vals) as cpu_correct
    from 
    (
      select 
      ts, cpu, user_id
      from cputime
      order by ts
    )
  group by user_id;