Summarize employee attendance data on a weekly basis

I need to summarize employee attendance data based on a weekly basis. Right
now my spreadsheets are setup for a monthly basis. The spreadsheets have all
the data in a daily format so it is there. The problem I am having is
summarizing it by a time frame, in this case a week. The current setup has no
time frame restriction, I have a new workbook for each month. Rather then
create another workbook to gather the data on a weekly basis and one for a
monthly basis I would rather use the current workbook.

Here is where it gets interesting. I need to summarize by department, shift,
and week. Looking for some ideas.
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These are just my opinions, please feel free to correct them if they are
wrong.

My solution would be to have a new column, which is weeknumber - this
could either use the weeknum function or could take us back to the
Sunday (for example) - the Sunday version would be

=AttendanceDay-day(AttendanceDay)

(replace AttendanceDay with the cell reference)

This gives you a column where all days in a given week are on the same
date, then you can use a pivot table to get your data out.