SQL & PL/SQL

I'm quering employees who participated in activity1 and activity2. I'm getting output as following. I would like to convert these two rows into one.

employee_number          activity1       activity2

1                                        yes               no

1                                        no                 yes

The same employee did activity1 and activity 2. However, it's showing in two separate rows. It's because I have a case statement as follows

select employee_number,

case when activity1 = 1 then 'Yes' else 'No' end activity1,

case when activity2 = 2 then 'Yes' else 'No' end activity2

from report_data

I need to see the output as below

employee_number          activity1       activity2

       1                    yes               yes

Please let me know as how can I get the above output.

Thanks in advance!