On 6/9/09 Tue Jun 9, 2009 1:24 AM, "Dave Tang" <d.t...@imb.uq.edu.au>
scribbled:
> Hello,
>
> I have a problem, which I have put into an analogy.
>
> Suppose a parent has 11 children. These children like chocolate. If 9 or
> more of the 11 children from the same parent like a particular chocolate,
> the parent will like the chocolate. I want to find out what types of
> chocolate each parent likes.
>
> I have a file listing each child's preference of chocolate (which can be
>> = 1). There are +45,000 parents, each parent has 11 children and there
> are +100,000 different types of chocolate.
>
> I guess I could parse the file and store the results in something like this
>
> $listOfParent{$parentOne}{$childOne} = @chocolate;
More precisely,
$listOfParent{$parentOne}{$childOne} = [ @chocolate ];
since hash elements must be scalars.
> ...
> $listOfParent{$parentOne}{$childN} = @chocolate;
> ...
> $listOfParent{$parentN}{$childN} = @chocolate;
>
> Then
>
> my %result = ();
> foreach my $parent (keys %listOfParent){
foreach my $parent (keys %$listOfParent) {
(note: $listOfParent and %listOfParent are two different variables)
> my $chocolate = '';
> foreach my $child (keys %{$listOfParent}{$parent}){
foreach my $child ( keys %{$listOfParent->{$parent}} ) {
(note: $listOfParent{$parent} is an element of %listOfParent, not an element
of the hash referenced by $listOfParent)
> foreach ($listOfParent{$parent}{$child}){
foreach ( $listOfParent->{$parent}->{$child} ) {
> $chocolate = $_;
> if (exists $result{$parent}{$chocolate}){
> $result{$parent}{$chocolate}++;
> } else {
> $result{$parent}{$chocolate} = '1';
> }
You can replace the above 5 lines with just this:
$result{$parent}->{$chocolate}++;
as Perl will treat an undef value as zero in an increment operation.
> }
> }
> }
>
> Then go through %result and print out the >=9. Is there a better way of
> doing this?
If you don't care about the names of the parents and children, you could use
an array of arrays instead of a hash-of-hashes to store the preference data.
Arrays will use a little less memory storage than hashes, and access will be
a little faster. If, however, you already have your hashes created for other
purposes, then converting to arrays will probably not help.
A little whitespace sprinkled into your source code makes it more readable,
which is always a good thing when you are looking for help.
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