#!/usr/bin/perl 

use strict;
use warnings;
use Data::Dumper;

my %groups;
$groups{'g1'} = ['a'..'g'];
$groups{'g2'} = ['h'..'n'];
$groups{'g3'} = ['o'..'u'];
$groups{'g4'} = ['v'..'z'];

my %lookup;
for my $grp (keys %groups){
  %{$lookup{$grp}} = map {$_ => undef} @{$groups{$grp}};
}

my %output;
while(my $line=<DATA>){
  chomp($line);
  my $usr=substr($line,8,2);
  my $time=substr($line,0,4); 
  my $username_string = substr($line,11);
  my @usernames= split ',', $username_string;
  for my  $name (@usernames){
    for my $grp (keys %lookup){
      $output{$time}{$grp}++ if exists $lookup{$grp}{$name};
    }
  }
}

for my $time (sort keys %output){
  print "$time\t";
  for my $grp (sort keys %groups){
    my $logged_in = 0;
    $logged_in = $output{$time}{$grp} 
      if exists $output{$time}{$grp};
    print "$logged_in ($grp) users\t";
  }
  print "are logged in\n";
}

__DATA__
1.00 50 10 x,y,z,w,u,e,g,j,k,a
1.10 50 13 x,y,b,a,g,j,k,r,,n,m,s,
1.20 50 05 c,t,g,q,f
1.50 50 08 a,t,y,w,z,x,s,b
2.00 50 14 x,y,u,b,g,f,s,a,i,o,p,c