use strict;
use warnings;

# Convert ( 1,2,3,7,9,10,11,12) to '1-3,7,9-12'.
#
# Handles duplicate numbers (by ignoring them), reals, out
# of order elements*, and changes in sign within the array.
#
# * Well, I guess I should say that it assumes you want
# 'normal' order and not necessarily the order given.
#
sub num2range( @ )
{
  my ( @end_points , @ranges );

  @_ = sort { $a <=> $b } @_;

  # Construct the first interval.
  $end_points[ 0 ] = $end_points[ 1 ] = shift;

  # We're done! ... Unless there's more than one element in
  # the array. :)
  @_ or return wantarray ? ( $end_points[ 0 ] ) : $end_points[ 0 ];

  # Scan through the rest of the array, building on the
  # current endpoint until we get to a jump.  Whereupon we
  # push the current endpoint into the list of ranges, and
  # initialize a new interval with the current element.
  for ( @_ )
  {
    if ( $_ - $end_points[ 1 ] == 1 ) { $end_points[ 1 ]++; }
    else
    {
      unless ( $_ == $end_points[ 1 ] )
      {
        push @ranges , ( $end_points[ 0 ] == $end_points[ 1 ] ) ?
                                             "$end_points[ 0 ]" :
                             "$end_points[ 0 ]-$end_points[ 1 ]";
      }
      @end_points = ( $_ , $_ );
    }
  }

  # The last element is special since it has no antecedant
  # and, hence, will never be processed by the push above.
  push @ranges , ( $end_points[ 0 ] == $end_points[ 1 ] ) ?
                                       "$end_points[ 0 ]" :
                       "$end_points[ 0 ]-$end_points[ 1 ]";

  return wantarray ? @ranges : join( ',' , @ranges );
}

# For example:
# print scalar num2range( 1,2,2.5,3.5,4.5,7,6,-5,-6,-7,7,8,9,10,0,12,42-24 );
# Gives:
# -7--5,0-2,2.5-4.5,4.6,6-10,12,18