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.

In reply to Re: Array Folding by davidrw
in thread Array Folding by BarMeister

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.