Pivot in oracle 10g for string

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Oracle

Hi All,

I have a table1:

name  |  sub  |  week|status
stu1  |  math |  1  |  yes
stu1  |  eng  |  1  |  
stu1  |  sci  |  1  |  no
stu1  |  math |  2  |  yes
stu1  |  eng  |  2  |  
stu1  |  sci  |  2  |  yes

I need a pivot like:

name  |  sub  |  week1 |  week2
stu1  |  math |  yes  |  yes
stu1  |  eng  |      |  
stu1  |  sci  |  no  |  yes

I need this output for both 11g and 10g (something that works for both).

What I have tried:

I had requirement of same output, only instead of 'yes' and 'no', there were numbers
Since the server has 10g, my query was roughly:

select name, sub,
sum(case when week=1 then case when sub='math' then status
                               when sub='eng' then status
                               when sub='sci' then status end end) as week1,
sum(case when week=2 then case when sub='math' then status 
                               when sub='eng' then status 
                               when sub='sci' then status end end) as week2
from(query for table1)
group by name, sub;

But here aggregate function is not working on strings 'yes' or 'no'.
Please help!!