in reply to Twisted sort requirements

Yes - this is VERY late to this party, but, this code should be relevant for reference.

I liked injunjoel's streightforward code, but I wanted to simplify it, and make special cases stand out. I also dislike handling special cases inside sort routines, because these are called more often than the number of items to be sorted. I also believe I have minimized the number of loops.

The only part I am not happy with is the "Special Marker" that is passed into the sort. That is a compromise made in order to simplify the code: 

#!/usr/bin/perl -w
use strict;
my @things_to_sort = (
                   { author => 'bart', title => 'skateboarding' },
                   { author => 'lisa', title => 'postmodernism' },
                   { author => 'marge', title => 'hairstyles' },
                   { author => 'lisa', title => 'THIS BOOK FIRST' },
                   { author => 'homer', title => 'donuts' },
                   { author => 'lisa', title => 'Eating Veggies' },
                   { author => 'bart', title => 'coolness' }
                  );
#this begs for a new structure.
#lets use a hash.
my (%authors_books,  $FirstAuth);
my $FirstTitle = "THIS BOOK FIRST";
my $Special_Low_Sort_Marker = "0x00" x 100; # A hundred nulls

#turn your AoH's into a HoA's
#Find first Author
#Mark Specially-named books
#see perldsc for reference
foreach (@things_to_sort){
    if ( $_->{title} eq $FirstTitle){
       $FirstAuth =  $_->{author} ;
       push @{$authors_books{ $_->{author} }},
            $Special_Low_Sort_Marker . $_->{title}; # Special Marker -
+ Push to top of SORT
    }else{
         push @{$authors_books{ $_->{author} }},    $_->{title};
    }  
}

#display the information.
if ($FirstAuth){
  PrintAuthor($FirstAuth);
  delete $authors_books{$FirstAuth};
}
foreach my $author ( sort keys %authors_books){
    PrintAuthor($author);
}
########################
sub PrintAuthor{
  my $author = shift;
  print "$author books:\n";
  foreach (sort @{$authors_books{$author}}){
       s/^$Special_Low_Sort_Marker//;     # Remove Special marker
       print "\t$_\n";
  }
}

[download]
I added an extra data line, to ensure that sorting was alpha, according the OP's spec. The output: 
lisa books:
        THIS BOOK FIRST
        Eating Veggies
        postmodernism
bart books:
        coolness
        skateboarding
homer books:
        donuts
marge books:
        hairstyles

[download]
Extending this to allow Multiple "First Authors" is left as an exercise for the reader.

     "For every complex problem, there is a simple answer ... and it is wrong." --H.L. Mencken

Replies are listed 'Best First'.
Re^2: Twisted sort requirements
by johngg (Canon) on Feb 02, 2006 at 15:01 UTC
    Another late one but never mind! I also adopted the extra data line. Then a pass through the data once to find who wrote "THIS BOOK FIRST" and the rest can be done in a Schwartzian transform. 
    #!/usr/local/bin/perl -w
#
use strict;

our @thingsToSort = (
   {author => 'bart', title => 'skateboarding'},
   {author => 'lisa', title => 'postmodernism'},
   {author => 'marge', title => 'hairstyles'},
   {author => 'lisa', title => 'THIS BOOK FIRST'},
   {author => 'homer', title => 'donuts'},
   {author => 'bart', title => 'coolness'},
   {author => 'lisa', title => 'eating veggies'});

our $firstAuthor = q();
foreach (@thingsToSort)
{
    next unless $_->{title} eq 'THIS BOOK FIRST';
    $firstAuthor = $_->{author};
    last;
}

print
   map {"$_->[0]->{author}: $_->[0]->{title}\n"}
   sort
   {
       $b->[1] <=> $a->[1] ||
       $b->[2] <=> $a->[2] ||
       $a->[0]->{author} cmp $b->[0]->{author} ||
       $a->[0]->{title} cmp $b->[0]->{title}
   }
   map
   {
       [
          $_,
          $_->{title} eq 'THIS BOOK FIRST',
          $_->{author} eq $firstAuthor
       ]
   }
   @thingsToSort;

    [download]
    I tried to think of a way to accomplish the first pass in the transform to make things simpler but failed.

    Cheers,

    JohnGG

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