in reply to Tricky Problem

It looks like you're trying to do something reminiscent of dealing with schedules or availablity, but that is just supposition. Your output, however, looks like it could be done with a complex data structure. (I have also included the data Jasper inquired about, to show how it would be handled by this untested sample code as well.) 

my (%data);
while (<DATA>) {
  chomp;
  # $_ contains '100-233,MA,150:250', for example
  my @initialparts = split( /,/, $_ );
  # @initialparts now contains ( '100-233', 'MA', '150:250' )
  my @leadparts = split( /-/, $initialparts[0]);
  # @leadparts now contains ( '100', '233' )
  push( @{$data{$leadparts[0]}{$initialparts[1]}{'items'}, 
      $leadparts[1] );
  # @{$data{'100'}{'MA'}{'items'} = ( '233' )
  if (scalar(@initialparts) > 2) {
    # Do only if there was a last term
    my @tailparts = split( /:/, $initialparts[2] );
    # @tailparts now contains ( '150', '250' )
    push( @{$data{$leadparts[0]}{$initialparts[1]}{'data'}, 
        @tailparts );
  }
}
open(OUTF, $0 . '.out') or die("Can't open $0.out for output: $!\n");
foreach my $f1 (sort(keys(%data))) {
  # Personally, I prefer data sorted, 
      # although you could leave out the sorts above, and following
  print $f1, "\n";
  foreach my $f2 (sort(keys(%{$data{$f1}}))) {
    print $f2, "\n";
    my $v4 = '|'
    if (defined($data{$f1}{$f2}{'data'} {
      $v4 .= join( ':', sort(@{$data{$f1}{$f2}{'data'}) );
    }
    foreach my $v3 (sort(@{$data{$f1}{$f2}{'items'})) {
      print $v3, $v4, "\n";
    }
  }
}
__DATA__
100-233,MA,150:250
100-344,MA,350:
200-400,ER,
200-300,ER,576
100-250,MA,150
75-300,MA,350

[download]

And now, a run, based on that data. 

#
# Variables, throughout run
#
# Read line 1
$_ = '100-233',MA,150:250
@initialparts = ( '100-233', 'MA', '150:250' )
@leadparts = ( '100', '233' )
%data = { '100' => { 'MA' => { 'items' => ( '233' ) }}}
@tailparts = ( '150', '250' )
$data = { '100' => { 'MA' => { 'items' => ( '233' ), 
                               'data' => ( '150', '250' ) }}}
# Read line 2
$_ = '100-344,MA,350:'
@initialparts = ( '100-344', 'MA', '350:' )
@leadparts = ( '100', '344' )
%data = { '100' => { 'MA' => { 'items' => ( '233', '344' ), 
                               'data' => ( '150', '250' ) }}}
@tailparts = ( '350' )
%data = { '100' => { 'MA' => { 'items' => ( '233', '344' ), 
                               'data' => ( '150', '250', '350' ) }}}
# Read line 3
$_ = '200-400,ER,'
@initialparts = ( '200-400', 'ER' )
@leadparts = ( '200', '400' )
%data = { '100' => { 'MA' => { 'items' => ( '233', '344' ), 
                               'data' => ( '150', '250', '350' ) }}, 
          '200' => { 'ER' => { 'items' => ( '400' ) }}}
# Read line 4
$_ = '200-300,ER,576'
@initialparts = ( '200-300', 'ER', '576' )
@leadparts = ( '200', '300' )
%data = { '100' => { 'MA' => { 'items' => ( '233', '344' ), 
                               'data' => ( '150', '250', '350' ) }}, 
          '200' => { 'ER' => { 'items' => ( '400', '300' ) }}}
@tailparts = ( '576' )
%data = { '100' => { 'MA' => { 'items' => ( '233', '344' ), 
                               'data' => ( '150', '250', '350' ) }}, 
          '200' => { 'ER' => { 'items' => ( '400', '300' ), 
                               'data' => ( '576' ) }}}
# Read line 5
$_ = '100-250,MA,150'
@initialparts = ( '100-250', 'MA', '150' )
@leadparts = ( '100', '250' )
%data = { '100' => { 'MA' => { 'items' => ( '233', '344', '250' ), 
                               'data' => ( '150', '250', '350' ) }}, 
          '200' => { 'ER' => { 'items' => ( '400', '300' ),
                               'data' => ( '576' ) }}}
@tailparts = ( '150' )
%data = { '100' => { 'MA' => { 'items' => ( '233', '344' ), 
                               'data' => ( '150', '250', '350', '150' 
+) }}, 
          '200' => { 'ER' => { 'items' => ( '400', '300' ), 
                               'data' => ( '576' ) }}}
# Read line 6
$_ = '75-300,MA,350'
@initialparts = ( '75-300', 'MA', '350' )
@leadparts = ( '75', '300' )
%data = { '75' =>  { 'MA' => { 'items' => ( '300' ) } },
          '100' => { 'MA' => { 'items' => ( '233', '344' ), 
                               'data' => ( '150', '250', '350', '150' 
+) }}, 
          '200' => { 'ER' => { 'items' => ( '400', '300' ),
                               'data' => ( '576' ) }}}
@tailparts = ( '350' )
%data = { '75'  => { 'MA' => { 'items' => ( '300' ), 
                               'data' => ( '350' ) }},
          '100' => { 'MA' => { 'items' => ( '233', '344' ), 
                               'data' => ( '150', '250', '350', '150' 
+) }}, 
          '200' => { 'ER' => { 'items' => ( '400', '300' ), 
                               'data' => ( '576' ) }}}
# In loop
%data = { '75'  => { 'MA' => { 'items' => ( '300' ), 
                               'data' => ( '350' ) }},
          '100' => { 'MA' => { 'items' => ( '233', '344' ), 
                               'data' => ( '150', '250', '350', '150' 
+) }}, 
          '200' => { 'ER' => { 'items' => ( '400', '300' ), 
                               'data' => ( '576' ) }}}
$f1 = '75'
$f2 = 'MA'
$v4 = '|350'
$v3 = '300'
$f1 = '100'
$f2 = 'MA'
$v4 = '|150:150:250:350'
$v3 = '233'
$v3 = '344'
$f1 = '200'
$f2 = 'ER'
$v4 = '|576'
$v3 = '300'
$v3 = '400'
#
# Output, from run
#
75
MA
300|350
100
MA
233|150:150:250:350
344|150:250:350
200
ER
300|576
400|576

[download]

If you do not wish duplicates in the last portion of the data, then you could do something like: 

    if (defined($data{$f1}{$f2}{'data'} {
      my (%uniq);
      foreach (@{$data{$f1}{$f2}{'data'}) {
        $uniq{$_}++;
      }
      $v4 .= join( ':', sort(keys(%uniq)) );
    }

[download]

Hope that helps.

Update: 19 Aug 2004

Added <readmore></readmore> tags around the run/variable trace.

In Section Seekers of Perl Wisdom