Array Folding

BarMeister has asked for the wisdom of the Perl Monks concerning the following question:

I am trying to take an array of hashes and based on certain values within the hash add elements of the array together and then shrink the array. Here is what I have so far:

sub fold {

    my $self = shift;
    return if ! @{$self->{data}};

    my $array = $self->{data};
    my $date_grouped = 0;
    my $campaign_grouped = 0;
    foreach(@{$self->{groups}}) {
        $date_grouped = 1 if $_ eq 'date';
        $campaign_grouped = 1 if $_ eq 'campaign';
    }

    my $merge_index = 0;
    my $points_needed = $campaign_grouped + $date_grouped;
    @$array = sort {fold_sort($campaign_grouped,$date_grouped)} @$arra
+y;
    for(my $current_index=0; $current_index<@$array; $current_index++)
+ {
        my $el = $array->[$current_index];
        if($merge_index == $current_index) {
            next;
        }

        #compare current element to merge element
        my $match = 0;
        my $merge = $array->[$merge_index];
        $match++ if $date_grouped &&
                $el->{date} eq $merge->{date};
        $match++ if $campaign_grouped &&
                $el->{campaign_id} == $merge->{campaign_id};

        #if we can fold the array elements then do so and remove the
        #current element
        if($match == $points_needed) {
            $merge->{views} += $el->{views};
            $merge->{clicks} += $el->{clicks};
            my $del = splice(@$array,$current_index,1);
            $current_index--;
        } else {
            $merge_index++;
        }
    }

}
[download]

Anyone have a better way of doing this? The fold_sort function just orders the array based on how were are grouping the elements. Thanks, Kenny

PS - I was not sure of what to call this so I figured "Array Folding" was a good enough term...if there is another term that people use let me know please :-)

Comment on Array Folding Download Code

Replies are listed 'Best First'.
Re: Array Folding by davidrw (Prior) on Mar 05, 2006 at 00:54 UTC
Re-reading OP again, i think i understood this time ... I believe (untested) that this does the same task: sub fold { my $self = shift; my $array = $self->{data}; return unless $array && @$array; my %groups = map { $_ => 1 } @{$self->{groups}; my @keys = grep { $groups{$_} } qw/ date campaign /; my %h; foreach my $el ( @$array ){ my $k = join ":", @{$_}{@keys}; # This only works if the +date & campaign values do not contain ':' if( exists $h{$k} ) { $h{$k}->{views} += $el->{views}; $h{$k}->{clicks} += $el->{clicks}; }else{ $h{$k} = $el; } } @$array = sort { fold_sort($groups{campaign},$groups{date}) } values + %h; } [download] Note that the basic approach is to hash up on the commonality (date and/or campaign) to combine everything, then take those values and sort for final result.	[reply] [d/l]
Re: Array Folding by borisz (Canon) on Mar 05, 2006 at 01:04 UTC
Here is my try: untested. propably you need to sort the keys for your output. And the keys in groups must match the data keys. say date and campain_id in your example. `sub fold { my $self = shift; my %h; my @groups = @{ $self->{groups} }; for ( @{ $self->{data} } ) { push @{ $h{ join $;, @$_{ @groups } } }, $_; } $self->{data} = [ map { my $x; @$x{ @groups } = @{ $h{$_}->[0] }{ @groups }; for ( @{ $h{$_} } ) { $x->{views} += $_->{views}; $x->{clicks} += $_->{clicks}; } $x; } keys %h ]; }` [download] Boris	[reply] [d/l]
Re^2: Array Folding by BarMeister (Beadle) on Mar 07, 2006 at 14:53 UTC
Thanks everyone for the feedback :-)	[reply]
Re: Array Folding by davidrw (Prior) on Mar 05, 2006 at 00:35 UTC
Can you show the source for `fold_sort()`? It's not clear to me why/who this line works, since the sort block isn't dependent upon `$a` or `$b` at all (in any obvious way).. `@$array = sort {fold_sort($campaign_grouped,$date_grouped)} @$arra +y;` [download] Can you also provide some data samples? Input, actual output, and desired output?	[reply] [d/l] [select]