I have 12 different excel files - monthly reports, with 24 fields
(columns) and between 26-27k records (rows) each month. Given the size
of each, it doesn't look like its feasible to combine the worksheets
into 1. Now, for each month I need to be able to:

1. filter the records based on column headings (either 1 or 2 headings
- city_type or city_type AND fare_type)
2. total another two columns to compute the sum; and
3. extract the result to a monthly summary based on the filters in 1

and I need to do this for all 12 months, preferably summarising in one
worksheet.

I tried using autofilter and then totalling to no avail - there are
too many city_types for me to do each month. Is there a
smarter way of doing this than spending hours doing this manually with
no guarantee of accuracy!