in reply to Re: How to loop over groups
in thread How to loop over groups

True. But it gets much worse when I'm printing out a header for the section, then the individual rows in that group, then the total. Thinking about it now, the trickiest part is knowing when to print out the next group's header. Is there any way to avoid using the "$old" temp variable to handle that? 
@a = (['a',1],['a',2],['b',3],['b',4]); # "db read"

my $old;
my $total = 0;                          # init
foreach my $row (@a) {
        if ($old && $old ne $row->[0]) {
                print "$old: $total\n"; # finish row block

                $total = 0;             # init
                print "Section $row->[0]\n";
        }    

        $total += $row->[1];            # processrow block
        print "$row->[1]\n";        

        $old = $row->[0];               # set temp variable
}
print "$old: $total\n";                 # finish row block

[download]

Replies are listed 'Best First'.
Re: Re: Re: How to loop over groups
by RMGir (Prior) on Apr 02, 2002 at 13:06 UTC
    Sure, just rearrange your data.

    By building a hash which groups the rows together, your problem goes away. 

    @a = (['a',1],['a',2],['b',3],['b',4]); # "db read"
my %aByGroup;

foreach(@a) {
  # you could just push $_->[1], but I'm guessing your
  # data is more complex, so I'm keeping the whole row
  push @{$aByGroup{$_->[0]}},$_;
}

my $old;
foreach my $group (sort keys %aByGroup) {
    my $total = 0;                          # init
    print "Section $group\n";

    foreach my $row(@{$aByGroup{$group}}) {
        $total += $row->[1];            # processrow block
        print "$row->[1]\n";        
    }

    print "$group: $total\n";           # finish row block
}

    [download]

    --
    Mike
[reply]
[d/l]

In Section Seekers of Perl Wisdom