I was perturbed by your post Sardushan. I'll
try to explain why.
Sudarshan Raghavan wrote:
> Rob Anderson wrote:
>
> > Hi Jeroen,
> >
> >
> >
> > > while (@values = $lcsr->fetchrow) {
> > >
> > >
> >
> > This is probably the root of your problem every time you go
> > through this loop, you are repopulating your array, put a my
> > before @values.
> >
>
> Why do you think this is a problem? All the my would do is create a
> new lexical @values in every iteration.
Yes, but I can see why Rob thought that it may be a problem. I'm sure
you can too given the rest of his post.
> What do you mean by repopulating @values? my @values = ... would
> also populate @values.
> Am I missing something?
You're missing the rest of his post, which we know you have seen
since you comment on it below. As Rob suspected, repopulating the
global array '@values' would be a problem if the loop pushed [EMAIL PROTECTED]
onto the stack each time.
>
> >
> >
> >
> > > $key = shift @values;
> > > $key.= shift @values;
> > >
> > > push @$ref_to_a, [EMAIL PROTECTED];
> > >
> > >
> >
> > I don't recognise this format, I'd have done this line as.
> > push @$ref_to_a, [EMAIL PROTECTED];
> >
>
> [EMAIL PROTECTED] creates an anonymous arrayref by copying the values
> stored in @values. perldoc perlref, perldoc perllol
>
> If you are going use this statement
> push @{$ref_to_a}, [EMAIL PROTECTED];
> your while condition must be while (my @values = ...)
See? You knew all along really.
Rob was trying his best to help without being used to using
an anonymous array constructor like this. His answer was valid
and he shouldn't be told otherwise.
> If you are going to use
> push @{$ref_to_a}, [EMAIL PROTECTED];
> you can leave the while condition as while (@values = ...)
...but no mention of all the more useful caveats that using a
lexical is preferable since its scope is local to the containing
block.
> Reason: 'shallow copying' vs 'deep copying'
> Read through this link
> http://www.stonehenge.com/merlyn/UnixReview/col30.html
How many computer scientists do you think would know what you
were talking about if you mentioned 'shallow' and 'deep' copying.
They're useful terms only in the context of the document you have
linked to.
> >
> > > if ($old_key ne $key) {
> > > $hash{$key} = $ref_to_a;
> > > my $ref_to_a = undef;
> > > }
> > > $old_key = $key;
> > > }
> > >
> > >
> >
> >
> > Having made these comments, I haven't really understood your
> > logic or the need for your, old_key values. I'd have done
> > something like the following.
> >
> > while (my @row_data = $lcsr->fetchrow ) {
> >
>
> while (my ($key1, $key2, @row_data) = $lcsr->fetchrow) {
Doesn't recreate the existing functionality without a subsequent
my $key = $key1.$key2
> > $key = shift @row_data;
> > $key.= shift @row_data;
> >
> > # create top level array if this is the first time we've seen
> > this key if (! defined $data{$key}) {$data{$key} = []}
> >
>
> This is not neccessary, when you assign to a non-existent hash key,
> perl will create the key for you
It is necessary, because the following lines won't work without it. You
need
push @{$data{$key}},[EMAIL PROTECTED]
instead, otherwise $array_def will be 'undef' and
push @{undef}, [EMAIL PROTECTED]
doesn't work.
> >
> > my $array_ref = $data{$key};
> > push(@$array_ref, [EMAIL PROTECTED]);
> >
> >
>
> You can replace the code inside the while block with
> push (@{$data{$key1 . $key2}}, [EMAIL PROTECTED]);
...and hope very hard that you don't get two separate instances
where
$key1 = 'AB', $key2 = 'C'
and
$key1 = 'A', $key2 = 'BC'
> Your final code will be
Whose?
> while (my ($key1, $key2, @row_data) = $lcsr->fetchrow) {
> push (@{$data{$key1 . $key2}}, [EMAIL PROTECTED]);
> }
>
This is paramountly a beginners group. I think Rob did a grand job
of helping here, and may well have solved Jeroen's problem without
further gloss. I believe there is a place for detailed analyses
but only for interest's sake. I would hope that I and all other
posters will only ever 'enquire', 'help', 'inform' or 'correct'.
I hope this post itself falls into the last category - I shall no
doubt find out if I'm wrong.
Cheers,
Rob
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