my $allkeys;
for  ( @{ $allusers } ) {
    my $user = $_->{'user'};
    if ( !exists $allkeys->{$user} ) {
        my $attributes = { 'amount'    => $_->{'amount'},
                           'duration'  => $_->{'duration'}
                         };
        $allkeys->{$user} = $attributes;
        
    } else {
        my $refAttributes              = $allkeys->{$user};
        $refAttributes->{'amount'}     += $_->{'amount'};
        $refAttributes->{'duration'}   += $_->{'duration'};
    }
}

my $finalArray;
while ((my $key, my $value) = each %{$allkeys}) {
   my $hash = {  'user'       => $key,
                 'amount'     => $value->{'amount'},
                 'duration'   => $value->{'duration'}
               };
   push @{$finalArray}, $hash;
}