my %values;

while (<DATA>) {
    my ($col, $val) = split;
    # store the sum and number of occurrences in a hashref
    $values{$col}[0] += $val;
    $values{$col}[1]++;
}

for my $col (sort keys %values) {
    print "$col ", $values{$col}[0] / $values{$col}[1], "\n";
}