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)} @$array;
	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++;
		}
	}

}