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4D v14.3

REDUCE SELECTION


REDUCE SELECTION ( {aTable ;} number )

Parameter	Type	Description
aTable	Table	Table for which to reduce the selection, or Default table, if omitted
number	Longint	Number of records to keep selected

Description

REDUCE SELECTION creates a new selection of records for aTable. The command returns the first number of records from the current selection table. REDUCE SELECTION is applied to the current selection of aTable in the current process. It changes the current selection of aTable for the current process; the first record of the new selection is the current record.

Note: If the statement REDUCE SELECTION(0) is executed, there is no longer any selection nor any current records in the aTable.

Example

The following example first finds the correct statistics for a worldwide contest among the dealers in over 20 countries. For each country, the 3 best dealers who have sold product worth more than $50,000 and who are among the 100 best dealers in the world are awarded a prize. With a few lines of code, this complex request can be executed by using indexed searches:

 CREATE EMPTY SET([Dealers];"Winners") ` Create an empty set

 SCAN INDEX([Dealers]Sales amount;100;<) ` Scan from the end of the index

 CREATE SET([Dealers];"100 best Dealers") ` Put the selected records in a set

 For($Country;1;Records in table([Countries])) ` For each Country

  ` Search for the dealers in this country

    QUERY([Dealers];[Dealers]Country=[Countries]Name;*) ` ...who sold for more than $50,000

    QUERY(&;[Dealers];[Dealers]Sales amount>=50000)

    CREATE SET([Dealers];"WinnerDealers") ` Put them in a set

  ` They should be in the group of 100 best dealers

    INTERSECTION("WinnerDealers";"100 best Dealers";"WinnerDealers")

    USE SET("WinnerDealers") ` Potential winners for the country

  ` Sort them by the results in descending order

    ORDER BY([Dealers];[Dealers]Sales amount;<)

    REDUCE SELECTION([Dealers];3) ` Take the 3 best Dealers

    CREATE SET([Dealers];"WinnerDealers") ` The winners for the country

  ` Put them in the worldwide winners list

    UNION("WinnerDealers";"TheWinners";"TheWinners")

 End for

 CLEAR SET("100 best Dealers") ` Don't need this set anymore

 CLEAR SET("WinnerDealers") ` Don't need this set anymore

 USE SET("The Winners") ` Here you have the Winners

 CLEAR SET("The Winners") ` Don't need this set anymore

 OUTPUT FORM([Dealers];"Prize letter") ` Select the letter

 PRINT SELECTION([Dealers]) ` Print the letters