How to make a report showing the number of logins of users belonging to public groups?

Hi,  I need to create a specific report that should show:  The number of logins to the system in the last 30 days by users belonging to public groups, grouped by public groups.    For example:  User_1 is member of Group_1 and has logged in 10 times, User_2 is member of Group_1 and Group_2 and has logged in 5 times. In the report, I'd like to see:    Group_1:      User_1: 10      User_2: 5  Group_2:      User_2: 5    Getting this data is easy using SOQL, but I have no idea how to do it using reports.   Please help me ;)     @Reports & Dashboards