use Statistics::Frequency;

my $string = '1,3,5,7,9,1,3,4,5,6,2,1,5,6,7,9';
my %count = Statistics::Frequency::->new(split /,/, $string)->frequencies;

print "$_: $count{$_}\n" for sort keys %count;

__END__
1: 3
2: 1
3: 2
4: 1
5: 3
6: 2
7: 2
9: 2