Excel: Date Operated Grouping

[Nefarious]

I have a series of initials for different dates. I want to group those initials (perhaps with separating commas) according to which week they fall into.

At the moment they all have individual dates but I want them to be grouped into more general date ranges.

 

[Nefarious]

Perhaps if I set the cells to be =If A3>=A23 AND A3<A24 where 23 is the begining of the week which the data falls into and A24 is the begining of the next week

How would I then get the cell to display the value of cell A4??