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use List::Util qw( sum );

...
    my $data = $data{$k};
    print $k, 0+@$data, sum(@$data)/@$data;
}

my %data;
while (<>) {
...
    my $data = $data{$k};
    print $k, $data->[0], $data->[1]/$data->[0];
}

my $last;
my $sum;
...
if (defined($last)) {
    print $last, $sum/$count;
}

perl -lane'
    $d{$F[0]}[0]++
...
    $, = "\t";
    print $_, $d{$_}[0], $d{$_}[1]/$d{$_}[0] for keys %d;
'