Column as arrays.. more efficient than columns?

Table is like

create table foo (
number int,
subset int,
value  int
)

select * from foo;
number | subset | value
1        1        1
1        2        2
1        3        10
1        4        3

current query is like

select number,
avg(case when subset = 1 then value else null end) as v1,
avg(case when subset = 2 then value else null end) as v2,
avg(case when subset = 3 then value else null end) as v3,
avg(case when subset = 4 then value else null end) as v4
from foo
group by number

results
------
number | v1 | v2 | v3 | v4
1         1   2    10   4


I'm thinking of denormalising it a bit and put it either as an array or
just create a new table with the end result like the above.

I just want to know which is more efficient. Users can just do a

select * from new_foo where number = 'X';


Thanks.