sorting - Keeping multiple orders in data.table in R -


i have transaction table 50m rows, few sample fields follow:

buyer_id  month day hour location seller_id

i need repeatedly sort table find popular sellers, locations, month etc. per buyer , create new summary table.

i need merge summary table transaction table find out sellers popular in top frequent locations etc.

each time, i'll have re-sort transaction table according several sets of columns. might end sorting setorder(transaction, user_id, month, location) several times.

i know data.table create order reference (kinda keep in hidden column), without copying table.

is there way store , refer these "hidden columns" explicitly, don't have resort data many times in same way?


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