Let me rephrase that: Also you seem to try to store duplicate keys in your hash ;-)

Naturally the 'my %hash' inside the loop prevents any data to accumulate in the hash (this as an explanation to the poster who started the thread), but I'm sure he had something else in mind for that hash. Not to say that I did spot that bug, I didn't

hello this is my first post. I think third column has some special meaning which I don't know. If treat rows with each third column value, how about like this?

use strict;
use warnings;

my @key=("key", "start", "end");
my @data=();
my $key_pre=0;

while(<DATA>) {
    my %hash;
    @hash{@key}=(split(/,/,$_))[2 .. 4];    #(key=>1, start=>23, end=>
+45)
    if ($key_pre != $hash{key} ){
        &proc_eachkey( \@data ) if $#data > 0;
        @data=();
    }
    $key_pre=$hash{key};
    push @data, {%hash};                    #copy hash value
}
&proc_eachkey( \@data ) if $#data > 0;      #for last key

sub proc_eachkey {
    my ($data)= @_;
    my ($start_pre, $end_pre)=(0,0);

    foreach my $h (@$data){
        if ($end_pre != $h->{start} + 1) {
            printf "%d,%d,%d\n",  $h->{key}, ($start_pre + 1), ($h->{s
+tart} -1);
        }
        printf "%d,%d,%d\n",  $h->{key}, $h->{start}, $h->{end};

        ($start_pre, $end_pre)=($h->{start}, $h->{end});
    }
}
__DATA__
1,34,1,23,45,2,2
35,45,1,56,78,1,1
46,56,1,88,101,2,2
57,68,2,13,34,4,3
69,78,2,45,56,1,3
[download]

nothing better than ikegami's one. regards.