id cluster_array
1  [1,2]
2  [2,3]
3  [4]

[1,2] [1,2,2,3]
[3]   [4]

with t as (select unnest(array[1,1,2,2,3]) id, unnest(array[1,2,2,3,4]) clst)
select id, array_agg(clst) from t group by id order by id