BEGIN { printf "%-8s %6s\n", "GROUP", "MEAN" }
!($2 in seen) { seen[$2] = 1; order[++n] = $2 }
{ sum[$2] += $3; count[$2]++ }
END { for (i = 1; i <= n; i++) {
    g = order[i]
    printf "%-8s %6.2f\n", g, sum[g] / count[g]
} }