#!/usr/bin/env perl

use strict;
use warnings;

use List::Util qw{sum};

my %data = (client => {}, all => {});
my $client = $data{client};
my $all = $data{all};

while (<DATA>) {
    my ($name, $amount) = split;
    push @{$client->{$name}{amounts}}, $amount;
}

for (sort keys %$client) {
    push @{$all->{clients}}, $_;
    $client->{$_}{total} = sum @{$client->{$_}{amounts}};
    $all->{total} += $client->{$_}{total};
}

for (keys %$client) {
    $client->{$_}{percent} = $client->{$_}{total} * 100 / $all->{total};
}

use Data::Dump;
dd \%data;

__DATA__
a 1
b 5
a 3
b 7
c 9
a 2

##</code><code>##

{
  all => { clients => ["a", "b", "c"], total => 27 },
  client => {
    a => { amounts => [1, 3, 2], percent => 22.2222222222222, total => 6 },
    b => { amounts => [5, 7], percent => 44.4444444444444, total => 12 },
    c => { amounts => [9], percent => 33.3333333333333, total => 9 },
  },
}