Essentially, if tracking a bunch of data as subitems within an item, and then attempting to roll up that data in different ways, the only ways currently are as sum, average, median, min, and max. There’s no way to also then filter that data to only bring in certain values based on additional criteria from another column on the subitems. For example, an easy way to visualize this would be a simple set of subitem columns showing:
With current mirror controls, it is possible to get summary values for the sum or average ike ‘78’ or ‘26’ for the number column, but if wanting to create a mirror that filters those results based on a third column (or more), then there isn’t a way to do that simply/cleanly within the mirror column functionality. I can’t easily lift out the sum of the ‘Number’ column for all subitems where ‘Binary’ = ‘Yes’ or for which a date meets specific criteria.
There is a workaround currently, that requires creating at least one additional formula column within the subitem that looks at the columns intended for filtering the results and then setting a new value (so doing an ‘if Binary = Yes, set value to be Number’ scenario that gets rolled up)… but this also requires creating an entirely new column on the subitem (which still cannot be hidden from view), instead of filtering it at the mirror column level instead. Which in turn, if wanting to have multiple such sorts/filters built into a table, will then require multiple formula subitem columns to format things prior to even summarizing them, instead of just creating multiple flexible mirror summaries off of the original base Number column instead.