将所有组合储存在数组中，并打印数组的长度。
awk -F, '{a[$2][$1]} END { for (i in a) { print i "," length(a[i]) } }' *.csv

我修改了你的输入样本，使输入的处理明显，它不做自动排序。

#!/bin/sh

DBG=0

BASE=`basename "$0" ".sh" `

TEST_INPUT1="${BASE}_input_1.txt"
TEST_INPUT2="${BASE}_input_2.txt"

cat >"${TEST_INPUT1}" <<-!EnDoFiNpUt
user1,app1
user10,app2
user1,app2
user2,app1
user3,app1
!EnDoFiNpUt

cat >"${TEST_INPUT2}" <<-!EnDoFiNpUt
user1,app1
user2,app1
user2,app5
user10,app2
user10,app1
user4,app4
!EnDoFiNpUt

cat "${TEST_INPUT1}" "${TEST_INPUT2}" |
awk -F "," -v dbg="${DBG}" 'BEGIN{
    ### initialize arrays
    split("", apps ) ;
    split("", usage ) ;
    split("", users ) ;

    ### initialize arrays counter
    indexApps=0 ;
    indexUsers=0 ;
}
{
    if( dbg == 1 ){ print "\nLINE:   ", $0 ; } ;
    hit=0 ;

    if( indexApps == 0 ){
        indexApps=1 ;
        apps[1]=$2 ;
        if( dbg == 1 ){ print "\t [0] new app -> ", apps[1] ; } ;

        indexUsers=1 ;
        usage[ indexApps, 1 ]=$2 ;
        usage[ indexApps, 2 ]=1 ;
        if( dbg == 1 ){ print "\t [0]", apps[ indexApps ], " -> ", usage[ indexApps, 2 ] ; } ;

        users[ indexApps, 1 ]=indexUsers ;
        users[ indexApps, indexUsers+1 ]=$1 ;
        if( dbg == 1 ){ print "\t [0] users[", indexApps, " , ", indexUsers+1 " ]  -> ", users[ indexApps, indexUsers+1 ] ; } ;
    }else{
        for( i=1 ; i <= indexApps ; i++ ){
            if( $2 == apps[i] ){
                hit=1 ;
                if( dbg == 1 ){ print "\t [1] users[i,1] = ", users[i,1] ; } ;

                hitU=0 ;
                for( j=1 ; j <= users[i, 1] ; j++ ){
                    if( users[i,j+1] == $1 ){
                        hitU=1 ;
                        if( dbg == 1 ){ print "\t [1]     exists -> ", users[i,j+1] ; } ;
                        break ;
                    } ;
                } ;
                if( hitU == 0 ){
                    if( dbg == 1 ){ print "\t [1] Hit:  usage BEFORE  ", apps[i], " -> ", usage[i,2] ; } ;
                    usage[i,2]++ ;
                    if( dbg == 1 ){ print "\t [1] Hit:                ", apps[i], " -> ", usage[i,2] ; } ;

                    indexUsers=users[i,1]+1 ;
                    if( dbg == 1 ){ print "\t [1] users[i,1] + 1 = ", indexUsers ; } ;
                    users[ i, 1 ]= indexUsers ;
                    users[ i, indexUsers+1 ]=$1 ;
                    if( dbg == 1 ){ print "\t [1] users[", i, " , ", indexUsers+1 " ]  -> ", users[ i, indexUsers+1 ] ; } ;
                } ;
                break ;
            } ;
        } ;

        if( hit == 0 ){
            if( dbg == 1 ){ print "\t [2] NO hit ------------------------------- START" ; } ;
            indexApps++ ;
            apps[ indexApps ]=$2 ;
            if( dbg == 1 ){ print "\t [2] new app -> ", apps[ indexApps ] ; } ;

            usage[ indexApps, 1 ]=$2 ;
            usage[ indexApps, 2 ]=1 ;
            if( dbg == 1 ){ print "\t [2]", apps[ indexApps ], " -> ", usage[ indexApps, 2 ] ; } ;

            indexUsers=users[ indexApps, 1 ]+1 ;
            if( dbg == 1 ){ print "\t [2] users[ indexApps, 1 ] + 1 = ", indexUsers ; } ;
            users[ indexApps, 1 ]= indexUsers ;
            users[ indexApps, indexUsers+1 ]=$1 ;
            if( dbg == 1 ){ print "\t [2] users[", indexApps, " , ", indexUsers+1 " ]  -> ", users[ indexApps, iindexUsers+1 ] ; } ;
            if( dbg == 1 ){ print "\t [2] NO hit ------------------------------- END" ; } ;
        } ;
    } ;
}END{
    print "Application Usage:" ;
    for( i=1 ; i <= indexApps ; i++ ){
        printf("  %s = %3d\t", usage[i,1], usage[i,2] ) ;
        for( j=1 ; j <= users[i,1] ; j++ ){
            printf("\t%s", users[i,j+1] ) ;
            if( j > 10 ){ break ; } ;
        } ;
        print "" ;
    } ;
}'

会话输出如下：

ericthered@OasisMega1:/WORKS$ ./test_47.sh
Application Usage:
  app1 =   4        user1   user2   user3   user10
  app2 =   2        user10  user1
  app5 =   1        user2
  app4 =   1        user4
ericthered@OasisMega1:/WORKS$