0: Here's a function I wrote to group consecutive sets of integers in to a tabular form.
1: 
2: ####
3: ##
4: ## my $table_hrf = consecutive( \@integers )
5: ##
6: ## Description: function to find consecutive integers
7: ##
8: ## Parameters: a reference to an array of integers
9: ##
10: ## Returns: table of sorted, grouped integers in the form of
11: ##
12: ##            base_integer => sequence_length
13: ##
14: ## For instance, the list
15: ##
16: ##  qw( 20 2 3 4 5 6 7 23 19 17 25 30 11 12 22 21 68 103829 24 18 );
17: ##
18: ## will sort to
19: ##
20: ##       2 => 5,
21: ##      11 => 1,
22: ##      17 => 8,
23: ##      30 => 0,
24: ##      68 => 0,
25: ##  103829 => 0
26: ##
27: ## which means
28: ##
29: ##  sequence(5): 2 to 7
30: ##  sequence(1): 11 to 12
31: ##  sequence(8): 17 to 25
32: ##  single: 30
33: ##  single: 68
34: ##  single: 103829
35: ##
36: ####
37: sub consecutive
38: {
39:   my $integer_arf = shift;
40: 
41:   my %table = ( );
42: 
43:   my $base = 0;
44:   my $previous = 0;
45: 
46:   foreach my $number ( sort numerically @{ $integer_arf } )
47:   {
48:     if( ( $number - 1 ) == $previous ) # if the current number is one greater
49:     {                                  # than the previous, increment our base
50:       $table{ $base }++;
51:     }
52:     else # we've found a new sequence
53:     {
54:       $table{ $number } = 0; # we're the base number, so set our adder to 0
55:       $base = $number;
56:     }
57: 
58:     $previous = $number; # end of loop -- our $number is now old
59:   }
60: 
61:   return \%table;
62: }
63: 
64: sub numerically { $a <=> $b }