REDUCE

The REDUCE command is used to reduce an isolation to its uniqueness, based on specified criteria.

Syntax:
                REDUCE/options collection [tablename] fieldname ... fieldname

                Notation standards              Options Answers

Options:
                X             -Suppress the command response
                Y             -Do not alter the command answer cells

Answers:
                Ctl.Ans1                -The "reduced to" value
                Ctl.Ans2                -The original number of records
                Ctl.Ans3                -Zero

Notes:
Suppose you want to send a mailing to your NEW YORK customers, but you don't want to send more than one to a household.

First isolate the NY customers. Then eliminate any duplicate addresses using the REDUCE command:

                FIND A CUSTOMERS WHERE STATE=NY
                REDUCE A CUSTOMERS STREET ZIP

All records that duplicate STREET and ZIP are now eliminated from the collection. Now you can sort them by ZIP and print labels:

                SORT A CUSTOMERS BY ZIP
                REPORT A CUSTOMERS ACCORDING TO LABELS

If you want to see the duplicates, the following will do the job:

                FIND A CUSTOMERS WHERE STATE=NY
                FIND B CUSTOMERS WHERE A
                REDUCE A CUSTOMERS STREET ZIP
                FIND C CUSTOMERS WHERE A XOR B

First get the NY customers in both A and B, then reduce A to the unique addresses. Now the A XOR B query isolates just the duplicates in C. That is, just the records those were in B and not in A.