a       Gallery 44
a       Gallery 52
b       Message 63
c       Gallery 100
c       Gallery 93
c       Message 62
a       Memo    72
a       Gallery 99
a       Message 60
b       Message 99

#!/bin/bash

set -eu
set -o pipefail

sort -k2,2  in.in > tmp

list=($(cut -f1 tmp | sort -u ))
domains=($(sort -k2,2  in.in | cut -f2 | sort -u))

for i in "${list[@]}"
do
    for domain in "${domains[@]}"
    do
        if grep -q -P "$i\t$domain" tmp; then
            grep -P "$i\t$domain" tmp > tmp2

            #   res=$(awk '{ total += $3; count++ } END { printf("%.0f\n", total/count); }' tmp2)
            res=$(awk '{ total += $3; count++ } END { print total/count }' tmp2)
            echo -e "$i\t$domain\t$res" >> res
        fi
    done

done

sort -k3 -n -r res -u  | head -n "${#domains[@]}"

#cat res
# echo -e "\n"
# for domain in "${domains[@]}"
# do
#     grep "$domain" res
# done


function clean {
    rm  tmp2 tmp res
}

trap clean EXIT