Re: most idiomatic way to iterate over an associative array?

On May 8, 2:02 pm, Urs Metzger <u..._at_ursmetzger.de> wrote:
> Mark D Powell schrieb:
>
>
>
> > On May 7, 4:07 am, Robert Klemme <shortcut..._at_googlemail.com> wrote:
> >> On May 7, 6:51 am, m..._at_pixar.com wrote:
>
> >>> This is what I'm doing now... is there a better way?
> >>> It would be great if there were some construct such
> >>> as 'for i in x begin ... end;'
> >>>     i := x.first;
> >>>     loop
> >>>         dbms_output.put_line(i);
> >>>         exit when i = x.last;
> >>>         i := x.next(i);
> >>>     end loop;
> >>> Many TIA!
> >>> Mark
> >> This will break for empty collections.  You can do
>
> >> SQL> set serverout on
> >> SQL> DECLARE  TYPE population_type IS TABLE OF NUMBER INDEX BY
> >> VARCHAR2(64);
> >>   2    continent_population population_type;
> >>   3    which VARCHAR2(64);
> >>   4  BEGIN
> >>   5    dbms_output.put_line('-----------');
> >>   6
> >>   7    which := continent_population.FIRST;
> >>   8    while which is not null loop
> >>   9      dbms_output.put_line(which || ' -> ' ||
> >> continent_population(which));
> >>  10      which := continent_population.NEXT(which);
> >>  11    end loop;
> >>  12
> >>  13    dbms_output.put_line('-----------');
> >>  14
> >>  15    continent_population('Australia') := 30000000;
> >>  16    continent_population('Antarctica') := 1000; -- Creates new
> >> entry
> >>  17    continent_population('Antarctica') := 1001; -- Replaces
> >> previous value
> >>  18
> >>  19    which := continent_population.FIRST;
> >>  20    while which is not null loop
> >>  21      dbms_output.put_line(which || ' -> ' ||
> >> continent_population(which));
> >>  22      which := continent_population.NEXT(which);
> >>  23    end loop;
> >>  24
> >>  25    dbms_output.put_line('-----------');
> >>  26  END;
> >>  27  /
> >> -----------
> >> -----------
> >> Antarctica -> 1001
> >> Australia -> 30000000
> >> -----------
>
> >> PL/SQL procedure successfully completed.
>
> >> SQL>
>
> >> Cheers
>
> >> robert
>
> >> seehttp://download.oracle.com/docs/cd/B19306_01/appdev.102/b14261/collec......
>
> > I think I would consider the For I in 1..n construct
>
> > UT1 > l
> >   1  declare
> >   2  type t_array is table of varchar2(10) index by binary_integer;
> >   3  t_list   t_array;
> >   4  begin
> >   5  t_list(1) := 'one';
> >   6  t_list(2) := 'two';
> >   7  t_list(3) := 'three';
> >   8  t_list(4) := 'four';
> >   9  t_list(5) := 'five';
> >  10  for I in 1..t_list.last loop
> >  11    dbms_output.put_line(t_list(I));
> >  12  end loop;
> >  13* end;
> > UT1 > /
> > one
> > two
> > three
> > four
> > five
>
> > PL/SQL procedure successfully completed.
>
> > Again as Robert warned in his solution the array should not be empty.
>
> > HTH -- Mark D Powell --
>
> Mark,
>
> this will work if - and only if - your array has no gaps:
>
> SQL> declare
>    2     type t_array is table of varchar2(10) index by binary_integer;
>    3     t_list   t_array;
>    4  begin
>    5     t_list(1) := 'one';
>    6     t_list(2) := 'two';
>    7     -- t_list(3) := 'three';
>    8     t_list(4) := 'four';
>    9     t_list(5) := 'five';
>   10     for I in 1..t_list.last loop
>   11        dbms_output.put_line(t_list(I));
>   12     end loop;
>   13  end;
>   14  /
> one
> two
> declare
> *
> ERROR at line 1:
> ORA-01403: no data found
> ORA-06512: at line 11
>
> your approach won't work for arrays with index by varchar2.
>
> The way to do is:
>
> SQL> declare
>    2     type t_array is table of varchar2(10) index by binary_integer;
>    3     t_list   t_array;
>    4     i        binary_integer;
>    5  begin
>    6     t_list(1) := 'one';
>    7     t_list(2) := 'two';
>    8     t_list(4) := 'four';
>    9     t_list(50) := 'fifty';
>   10
>   11     i := t_list.first;
>   12     while i is not null loop
>   13        dbms_output.put_line(t_list(I));
>   14        i := t_list.next(i);
>   15     end loop;
>   16  end;
>   17  /
> one
> two
> four
> fifty
>
> This will also work with empty collections or varchar2 indexes.
>
> Hth,
> Urs Metzger- Hide quoted text -
>
> - Show quoted text -

The recommendation to use table.next to move throught the array is an excellent point whenever the array could be empty or have holes in it. Most of the time the arrays I have worked with are populated earlier in the code so there are never gaps between first and last. Still one should always try to write code that will work in all possible circumstances and not just with the data in front of you.

Thanks.
-- Mark D Powell -- Received on Sat May 10 2008 - 09:08:54 CDT