1/2/2007, 1, 4, 5, 6
1/3/2007, 2, 5, 7, 10
1/5/2007, 5, 6, 8, 11

##</code><code>##

my @previous;
while(<>){
    chomp;
    my @current = split /,/, $_;
    if ( not @previous ) {
        print join ',', @current[ 1 .. $#current ];
        print "\n";
    }
    else {
        for my $i ( 1 .. ( $#current - 1 ) ) {
            print $current[$i], '-', $previous[$i], ',';
        }
        print $current[-1], '-', $previous[-1], "\n";
        @previous = @current;
    }
}