PL/SQL - Discarding duplicates when processing an array of data by maintaining a hashset (technically a map) of processed inputs

hashset_demo.sql

/*

This PL/SQL block demonstrates the use of an associative array and
the STANDARD_HASH function to discard duplicates when processing
an array of inputs from a PL/SQL array (VARRAY).

Written for & tested on an Oracle 12c database.

*/

DECLARE
    TYPE t_hashmap IS
        TABLE OF BOOLEAN INDEX BY VARCHAR2(40);
    v_map      t_hashmap;

    v_hash     VARCHAR2(40);

    TYPE t_arr_varchar2 IS
        VARRAY ( 5 ) OF VARCHAR2(100);
    v_inputs   t_arr_varchar2;
BEGIN

    v_inputs := t_arr_varchar2('One','Two','One','Four','Two');

    FOR i IN 1..v_inputs.count LOOP

        SELECT standard_hash( v_inputs(i) )
        INTO v_hash
        FROM dual;

        IF v_map.EXISTS(v_hash) THEN
            CONTINUE;
        END IF;

        v_map(v_hash) := true;

        dbms_output.put_line('Take Action on ' || v_inputs(i) );

    END LOOP;

END;
/